Donald J. Trump’s trial will continue Monday in a New York courtroom with him on the witness stand, part of a proceeding that threatens the business empire that underpins his public persona and that fostered his run for the White House.

The trial stems from a lawsuit brought by New York’s attorney general, Letitia James, which accuses Mr. Trump and other defendants, including his companies and sons Donald Jr. and Eric, of fraudulently inflating the value of assets to obtain favorable loans and insurance deals.

For the past five weeks, lawyers from the attorney general’s office have argued that Mr. Trump’s employees arbitrarily assigned values to individual assets to arrive at the former president’s desired net worth. Mr. Trump’s attorneys have responded that the assets had no objective value and that differing valuations are standard in real estate.

The judge, Arthur F. Engoron, ruled even before the trial that Mr. Trump and the other defendants were liable for fraud, and that their annual financial statements were filled with examples of such misconduct.

When the trial ends, Justice Engoron will decide whether Mr. Trump pays a significant penalty or is subject to any other punishment. Ms. James has asked that he pay $250 million and that he and his sons be permanently barred from running a business in New York.

Mr. Trump, a Republican, has denied all wrongdoing. After his testimony on Monday, his daughter Ivanka is scheduled to testify on Wednesday. The attorney general’s office is then expected to rest its case.

Mr. Trump’s attorneys will then present a defense. They are expected to recall many witnesses who have already testified, including the defendants, and to call their own experts. The trial is scheduled to last until Dec. 22, but may conclude before then.

Here is what has happened so far:

During the first week of the trial, Justice Engoron ordered Mr. Trump not to comment on members of the judge’s staff on social media. The admonition came in response to a post by Mr. Trump showing a picture of the judge’s clerk, Allison Greenfield, with Chuck Schumer, the Senate majority leader, mocking her as “Schumer’s girlfriend.”

A copy of the post remained on Mr. Trump’s campaign website. On Oct. 20, Justice Engoron called it a “blatant violation” and fined Mr. Trump $5,000.

The next week, Mr. Trump told reporters outside the courtroom that Justice Engoron has “a person who’s very partisan sitting alongside him, perhaps even much more partisan than he is.” Justice Engoron fined him $10,000.

On Friday, Mr. Trump’s legal team continued these attacks, saying communications between the judge and his clerk while court was in session created a “perception of bias” that might result in a mistrial.

A few hours later, Justice Engoron prohibited all attorneys from making statements about internal and confidential communications between him and his staff.

Engoron argued that the safety of his staff outweighed the First Amendment rights of the defendants, and wrote that his office had been “inundated with hundreds of harassing and threatening phone calls, voice mails, emails, letters and packages” since the trial began.

Twenty-three witnesses have testified, including four defendants: the Trump Organization’s former controller, Jeffrey McConney; the former chief financial officer, Allen Weisselberg; and Mr. Trump’s sons. Through documentary evidence like spreadsheets and emails, the attorney general’s team has tried to show the defendants’ intent to inflate Mr. Trump’s financial statements and have financial institutions rely on them.

Mr. McConney testified that some of his valuations were the result of a mistake or oversight, but others were intentional, such as a failure to account for 12 rent-stabilized apartments in the valuation of Trump Park Avenue.

Mr. McConney said that he did not act alone. He said that he arrived at inflated values or repeated them after conversations with Mr. Weisselberg.

On the witness stand, Mr. Weisselberg acknowledged his role in some of the manipulation of Mr. Trump’s assets. He also implicated his former boss, saying that Mr. Trump reviewed the financial statements before they were made final.

Both Trump sons tried to distance themselves from the financial statements. Over three days of testimony last week, the attorney general’s office tried to chip away at their claims.

Eric Trump said he didn’t concentrate on valuations, but was confronted with emails showing his active participation in the appraisal of Trump Organization assets. The attorney general’s office also tried to show that he ignored an independent estimate of the value of the family’s golf club in Westchester County, N.Y.

Donald Trump Jr. was presented with evidence to demonstrate his awareness of discrepancies in the valuations. He was shown an email he received from Forbes magazine alerting him to errors in a financial statement. But shortly after, he had told his accountants that the document contained no material misstatements.

Donald Trump Jr. was also confronted with his signature on letters in which he assumed responsibility for the financial statements, and at one point testified that he expected the company’s biggest lender to rely on their accuracy.