When President Donald J. Trump’s eldest son took the stage outside the Georgia Republican Party headquarters two days after the 2020 election, he likened what lay ahead to mortal combat.

“Americans need to know this is not a banana republic!” Donald Trump Jr. shouted, claiming that Georgia and other swing states had been overrun by wild electoral shenanigans. He described tens of thousands of ballots that had “magically” shown up around the country, all marked for Joseph R. Biden Jr., and others dumped by Democratic officials into “one big box” so their authenticity could not be verified.

Mr. Trump told his father’s supporters at the news conference — who broke into chants of “Stop the steal!” and “Fraud! Fraud!” — that “the number one thing that Donald Trump can do in this election is fight each and every one of these battles, to the death!”

Over the two months that followed, a vast effort unfolded on behalf of the lame-duck president to overturn the election results in swing states across the country. But perhaps nowhere were there as many attempts to intervene as in Georgia, where Fani T. Willis, the district attorney of Fulton County, is now poised to bring an indictment for a series of brazen moves made on behalf of Mr. Trump in the state after his loss and for lies that the president and his allies circulated about the election there.

Mr. Trump has already been indicted three times this year, most recently in a federal case brought by the special prosecutor Jack Smith that is also related to election interference. But the Georgia case may prove the most expansive legal challenge to Mr. Trump’s attempts to cling to power, with nearly 20 people informed that they could face charges.

It could also prove the most enduring: While Mr. Trump could try to pardon himself from a federal conviction if he were re-elected, presidents cannot pardon state crimes.

Perhaps above all, the Georgia case assembled by Ms. Willis offers a vivid reminder of the extraordinary lengths taken by Mr. Trump and his allies to exert pressure on local officials to overturn the election — an up-close portrait of American democracy tested to its limits.

There was the infamous call that the former president made to Brad Raffensperger, Georgia’s Republican secretary of state, during which Mr. Trump said he wanted to “find” nearly 12,000 votes, or enough to overturn his narrow loss there. Mr. Trump and his allies harassed and defamed rank-and-file election workers with false accusations of ballot stuffing, leading to so many vicious threats against one of them that she was forced into hiding.

They deployed fake local electors to certify that Mr. Trump had won the election. Within even the Justice Department, an obscure government lawyer secretly plotted with the president to help him overturn the state’s results.

And on the same day that Mr. Biden’s victory was certified by Congress, Trump allies infiltrated a rural Georgia county’s election office, copying sensitive software used in voting machines throughout the state in their fruitless hunt for ballot fraud.

The Georgia investigation has encompassed an array of high-profile allies, from the lawyers Rudolph W. Giuliani, Kenneth Chesebro and John Eastman, to Mark Meadows, the White House chief of staff at the time of the election. But it has also scrutinized lesser-known players like a Georgia bail bondsman and a publicist who once worked for Kanye West.

As soon as Monday, there could be charges from a Fulton County grand jury after Ms. Willis presents her case to them. The number of people indicted could be large: A separate special grand jury that investigated the matter in an advisory capacity last year recommended more than a dozen people for indictment, and the forewoman of the grand jury has strongly hinted that the former president was among them.

If an indictment lands and the case goes to trial, a regular jury and the American public will hear a story that centers on nine critical weeks from Election Day through early January in which a host of people all tried to push one lie: that Mr. Trump had secured victory in Georgia. The question before the jurors would be whether some of those accused went so far that they broke the law.

It did not take long for the gloves to come off.

During the Nov. 5 visit by Donald Trump Jr., the Georgia Republican Party was already fracturing. Some officials believed they should focus on defending the seats of the state’s two Republican senators, Kelly Loeffler and David Perdue, who were weeks away from runoff elections, rather than fighting a losing presidential candidate’s battles.

But according to testimony before the Jan. 6 committee by one of the Trump campaign’s local staffers, Mr. Trump’s son was threatening to “tank” those Senate races if there was not total support for his father’s effort. (A spokesman for Donald Trump Jr. disputed that characterization, noting that the former president’s son later appeared in ads for the Senate candidates.)

Four days later, the two senators called for Mr. Raffensperger’s resignation. The Raffensperger family was soon barraged with threats, leading his wife, Tricia, to confront Ms. Loeffler in a text message: “Never did I think you were the kind of person to unleash such hate and fury.”

Four other battleground states had also flipped to Mr. Biden, but losing Georgia, the only Deep South state among them, seemed particularly untenable for Mr. Trump. His margin of defeat there was one of the smallest in the nation. Republicans controlled the state, and as he would note repeatedly in the aftermath, his campaign rallies in Georgia had drawn big, boisterous crowds.

By the end of November, Mr. Trump’s Twitter feed had become a font of misinformation. “Everybody knows it was Rigged” he wrote in a tweet on Nov. 29. And on Dec. 1: “Do something @BrianKempGA,” he wrote, referring to Gov. Brian Kemp of Georgia, a Republican. “You allowed your state to be scammed.”

But these efforts were not gaining traction. Mr. Raffensperger and Mr. Kemp were not bending. And on Dec. 1, Mr. Trump’s attorney general, William P. Barr, announced that the Department of Justice had found no evidence of voting fraud “on a scale that could have effected a different outcome in the election.”

It was time to turn up the volume.

Mr. Giuliani was on the road, traveling to Phoenix and Lansing, Mich., to meet with lawmakers to convince them of fraud in their states, both lost by Mr. Trump. Now, he was in Atlanta.

Even though Mr. Trump’s loss in Georgia had been upheld by a state audit, Mr. Giuliani made fantastical claims at a hearing in front of the State Senate, the first of three legislative hearings in December 2020.

He repeatedly asserted that machines made by Dominion Voting Systems had flipped votes from Mr. Trump to Mr. Biden and changed the election outcome — false claims that became part of Dominion defamation suits against Fox News, Mr. Giuliani and a number of others.

Mr. Giuliani, then Mr. Trump’s personal lawyer, also played a video that he said showed election workers pulling suitcases of suspicious ballots from under a table to be secretly counted after Republican poll watchers had left for the night.

He accused two workers, a Black mother and daughter named Ruby Freeman and Wandrea Moss, of passing a suspicious USB drive between them “like vials of heroin or cocaine.” Investigators later determined that they were passing a mint; Mr. Giuliani recently admitted in a civil suit that he had made false statements about the two women.

Other Trump allies also made false claims at the hearing with no evidence to back them up, including that thousands of convicted felons, dead people and others unqualified to vote in Georgia had done so.

John Eastman, a lawyer advising the Trump campaign, claimed that “the number of underage individuals who were allowed to register” in the state “amounts allegedly up to approximately 66,000 people.”

That was not remotely true. During an interview last year, Mr. Eastman said that he had relied on a consultant who had made an error, and there were in fact about 2,000 voters who “were only 16 when they registered.”

But a review of the data he was using found that Mr. Eastman was referring to the total number of Georgians since the 1920s who were recorded as having registered before they were allowed. Even that number was heavily inflated due to data-entry errors common in large government databases.

The truth: Only about a dozen Georgia residents were recorded as being 16 when they registered to vote in 2020, and those appeared to be another data-entry glitch.

In the meantime, Mr. Trump was working the phones, trying to directly persuade Georgia Republican leaders to reject Mr. Biden’s win.

He called Governor Kemp on Dec. 5, a day after the Trump campaign filed a lawsuit seeking to have the state’s election results overturned. Mr. Trump pressured Mr. Kemp to compel lawmakers to come back into session and brush aside the will of the state’s voters.

Mr. Kemp, who during his campaign for governor had toted a rifle and threatened to “round up illegals” in an ad that seemed an homage to Mr. Trump, rebuffed the idea.

Two days later, Mr. Trump called David Ralston, the speaker of the Georgia House, with a similar pitch. But Mr. Ralston, who died last year, “basically cut the president off,” a member of the special grand jury in Atlanta who heard his testimony later told The Atlanta Journal Constitution. “He just basically took the wind out of the sails.”

By Dec. 7, Georgia had completed its third vote count, yet again affirming Mr. Biden’s victory. But Trump allies in the legislature were hatching a new plan to defy the election laws that have long been pillars of American democracy: They wanted to call a special session and pick new electors who would cast votes for Mr. Trump.

Never mind that Georgia lawmakers had already approved representatives to the Electoral College reflecting Biden’s win in the state, part of the constitutionally prescribed process for formalizing the election of a new president. The Trump allies hoped that the fake electors and the votes they cast would be used to pressure Vice President Mike Pence not to certify the election results on Jan. 6.

Mr. Kemp issued a statement warning them off: “Doing this in order to select a separate slate of presidential electors is not an option that is allowed under state or federal law.”

Rather than back down, Mr. Trump was deeply involved in the emerging plan to enlist slates of bogus electors.

Mr. Trump called Ronna McDaniel, the head of the Republican National Committee, to enlist her help, according to Ms. McDaniel’s House testimony. By Dec. 13, as the Supreme Court of Georgia rejected an election challenge from the Trump campaign, Robert Sinners, the Trump campaign’s local director of Election Day operations, emailed the 16 fake electors, directing them to quietly meet in the capitol building in Atlanta the next day.

Mr. Trump’s top campaign lawyers were so troubled by the plan that they refused to take part. Still, the president tried to keep up the pressure using his Twitter account. “What a fool Governor @BrianKempGA of Georgia is,” he wrote in a post just after midnight on Dec. 14, adding, “Demand this clown call a Special Session.”

Later that day, the bogus electors met at the Statehouse. They signed documents that claimed they were Georgia’s “duly elected and qualified electors,” even though they were not.

In the end, their effort was rebuffed by Mr. Pence.

In his testimony to House investigators, Mr. Sinners later reflected on what took place: “I felt ashamed,” he said.

With other efforts failing, the White House chief of staff, Mark Meadows, got personally involved. Just before Christmas, he traveled to suburban Cobb County, Ga., during its audit of signatures on mail-in absentee ballots, which had been requested by Mr. Kemp.

Mr. Meadows tried to get into the room where state investigators were verifying the signatures. He was turned away. But he did meet with Jordan Fuchs, Georgia’s deputy secretary of state, to discuss the audit process.

During the visit, Mr. Meadows put Mr. Trump on the phone with the lead investigator for the secretary of state’s office, Frances Watson. “I won Georgia by a lot, and the people know it,” Mr. Trump told her. “Something bad happened.”

Byung J. Pak, the U.S. attorney in Atlanta at the time, believed that Mr. Meadows’s visit was “highly unusual,” adding in his House testimony, “I don’t recall that ever happening in the history of the U.S.”

In Washington, meanwhile, a strange plot was emerging within the Justice Department to help Mr. Trump.

Mr. Barr, one of the most senior administration officials to dismiss the claims of fraud, had stepped down as attorney general, and jockeying for power began. Jeffrey Clark, an unassuming lawyer who had been running the Justice Department’s environmental division, attempted to go around the department’s leadership by meeting with Mr. Trump and pitching a plan to help keep him in office.

Mr. Clark drafted a letter to lawmakers in Georgia, dated Dec. 28, falsely claiming that the Justice Department had “identified significant concerns” regarding the state’s election results. He urged the lawmakers to convene a special session — a dramatic intervention.

Richard Donoghue, who was serving as acting deputy attorney general, later testified that he was so alarmed when he saw the draft letter that he had to read it “twice to make sure I really understood what he was proposing, because it was so extreme.”

The letter was never sent.

Still, Mr. Trump refused to give up. It was time to reach the man who was in charge of election oversight: Mr. Raffensperger, Georgia’s secretary of state.

On Jan. 2, he called Mr. Raffensperger and asked him to recalculate the vote. It was the call that he would later repeatedly defend as “perfect,” an hourlong mostly one-sided conversation during which Mr. Raffensperger politely but firmly rejected his entreaties.

“You know what they did and you’re not reporting it,” the president warned, adding, “you know, that’s a criminal — that’s a criminal offense. And you know, you can’t let that happen. That’s a big risk to you.”

Mr. Raffensperger was staggered. He later wrote that “for the office of the secretary of state to ‘recalculate’ would mean we would somehow have to fudge the numbers. The president was asking me to do something that I knew was wrong, and I was not going to do that.”

Mr. Trump seemed particularly intent on incriminating the Black women working for the county elections office, telling Mr. Raffensperger that Ruby Freeman — whom he mentioned 18 times during the call — was “a professional vote-scammer and hustler.”

“She’s one of the hot items on the internet, Brad,” Mr. Trump said of the viral misinformation circulating about Ms. Freeman, which had already been debunked by Mr. Raffensperger’s aides and federal investigators.

Trump-fueled conspiracy theories about Ms. Freeman and her daughter, Ms. Moss, were indeed proliferating. In testimony to the Jan. 6 committee last year, Ms. Moss recounted Trump supporters forcing their way into her grandmother’s home, claiming they were there to make a citizen’s arrest of her granddaughter; Ms. Freeman said that she no longer went to the grocery store.

Then, on Jan. 4, Ms. Freeman received an unusual overture.

Trevian Kutti, a Trump supporter from Chicago who had once worked as a publicist for Kanye West, persuaded Ms. Freeman to meet her at a police station outside Atlanta. Ms. Freeman later said that Ms. Kutti — who told her that “crisis is my thing,” according to a video of the encounter — had tried to pressure her into saying she had committed voter fraud.

“There is nowhere I feel safe. Nowhere,” Ms. Freeman said in her testimony, adding, “Do you know how it feels to have the president of the United States target you?”

On Jan. 7, despite the fake electors and the rest of the pressure campaign, Mr. Pence certified the election results for Mr. Biden. The bloody, chaotic attack on the Capitol the day before did not stop the final certification of Biden’s victory, but in Georgia, the machinations continued.

In a quiet, rural county in the southeastern part of the state, Trump allies gave their mission one more extraordinary try.

A few hours after the certification, a small group working on Mr. Trump’s behalf traveled to Coffee County, about 200 miles from Atlanta. A lawyer advising Mr. Trump had hired a company called SullivanStrickler to scour voting systems in Georgia and other states for evidence of fraud or miscounts; some of its employees joined several Trump allies on the expedition.

“We scanned every freaking ballot,” Scott Hall, an Atlanta-area Trump supporter and bail bondsman who traveled to Coffee County with employees of the company on Jan. 7, recalled in a recorded phone conversation. Mr. Hall said that with the blessing of the Coffee County elections board, the team had “scanned all the equipment” and “imaged all the hard drives” that had been used on Election Day.

A law firm hired by SullivanStrickler would later release a statement saying of the company, “Knowing everything they know now, they would not take on any further work of this kind.”

Others would have their regrets, too. While Mr. Trump still pushes his conspiracy theories, some of those who worked for him now reject the claims of rigged voting machines and mysterious ballot-stuffed suitcases. As Mr. Sinners, the Trump campaign official, put it in his testimony to the Jan. 6 committee last summer, “It was just complete hot garbage.”

By then, Ms. Willis’s investigation was well underway.

“An investigation is like an onion,” she said in an interview soon after her inquiry began. “You never know. You pull something back, and then you find something else.”