The indictments of Donald J. Trump — past and pending — are becoming the background music of the 2024 presidential campaign: always there, shaping the mood, yet not fully the focus.

Like so much of the Trump presidency itself, the extraordinary has become so flattened that Mr. Trump’s warning on Tuesday that he was facing a possible third indictment this year, this time over his involvement in the events that led to the Jan. 6 storming of the Capitol, drew shrugs from some quarters of his party and a muddled response from his rivals.

At one Republican congressional fund-raising lunch on Tuesday in Washington, the news of a likely third Trump indictment went entirely unmentioned, an attendee said. Some opposing campaigns’ strategists all but ignored the development. And on Capitol Hill, Mr. Trump’s allies quickly resumed their now-customary defensive positions.

Two and half years ago, the deadly riot that left the nation’s seat of government defiled had threatened to forever tarnish Mr. Trump’s political legacy. His supporters had stormed the Capitol to stop the certification of his defeat, stoked by their leader who had urged them to “fight like hell.” Even long-loyal Republicans broke with him as shattered glass littered the Capitol complex.

Yet today, Mr. Trump is the undisputed front-runner for the Republican Party’s 2024 presidential nomination. And the threatened charges relating to Jan. 6 against Mr. Trump were instead turned into attacks on his successor by his Republican defenders on Tuesday.

“We have yet again another example of Joe Biden’s weaponized Department of Justice targeting his top political opponent, Donald Trump,” Representative Elise Stefanik, the No. 4 House Republican, told reporters on Capitol Hill.

When Mr. Trump and Ms. Stefanik spoke by phone on Tuesday, the former president lingered on the line as they discussed ways to use the Republican-led House committees to try to attack the investigations. Mr. Trump also spoke with House Speaker Kevin McCarthy, who accused the Biden administration of trying to “weaponize government to go after their No. 1 opponent.”

Their comments reprised a role that Republicans in Congress played for Mr. Trump twice before when he was impeached, and twice again when he was indicted earlier this year. The first indictment came in March, by the district attorney in Manhattan in connection with hush money payments to a porn star. The second was in June, when he was indicted on charges of keeping top-secret classified documents and obstructing efforts to get them back.

Republicans and Mr. Trump’s extended orbit have established a rhythm of how to respond. Yet on the campaign trail, Mr. Trump’s leading rivals continue to struggle to even articulate a response.

Chief among them is Gov. Ron DeSantis of Florida, Mr. Trump’s top-polling rival. At a stop in South Carolina, Mr. DeSantis on Tuesday said that Mr. Trump “should have come out more forcefully” against the protesters who stormed the Capitol that day.

But after that line was picked up by Trump surrogates to attack Mr. DeSantis, his usually forceful DeSantis War Room Twitter account was anything but warring, accusing those surrogates of taking the governor out of context.

“I hope he doesn’t get charged,” Mr. DeSantis said of Mr. Trump in an interview broadcast later on CNN.

The CNN interview was supposed to be an important moment for a candidate who had previously avoided any sit-downs that might legitimize the “corporate media” that he regularly denounces. Instead, the network interrupted its own exclusive recorded DeSantis interview with live updates from outside a courthouse in Florida on one Mr. Trump’s coming trials. The sequence seemed to capture the state of the race that Mr. Trump is dominating.

Justin Clark, who served as Mr. Trump’s deputy campaign manager in 2020 and whose firm, National Public Affairs, has conducted polling of the primary race, said the challenge for his rivals is the voters themselves. Data from Mr. Clark’s firm shows that Republicans view an attack on Mr. Trump “as an attack on them,” he said.

“That loyalty is not something that is easy to beat in a campaign,” he added. “His opponents see this, too, and that is why they tread very carefully. It’s hard to see how another Republican breaks out when primary voters are rallying around their most recent president and any challengers have to hold their fire.”

Mr. Trump on Tuesday revealed that he had received a “target letter” from the Justice Department’s special counsel, Jack Smith, who is investigating his role in the lead-up to the violence of Jan. 6.

“Almost always means arrest and indictment,” Mr. Trump wrote of the target letter on Truth Social.

Mr. Smith’s office already indicted Mr. Trump in federal court in June, saying he had possessed reams of national defense material and obstructed the investigation. In the coming weeks, he faces possible indictment in Georgia related to efforts to overturn the 2020 election in that state.

Alyssa Farah Griffin, who had served as Mr. Trump’s communications director before resigning in late 2020 and publicly breaking with her former boss, said, “The most striking thing to me is that most of Trump’s G.O.P. opponents, who are polling double digits behind him, still will not seize this opportunity to denounce his unfit actions.”

One reason is that Mr. Trump, and Republican primary voters, have so thoroughly rewritten the history of Jan. 6, 2021. The mere mention of the day is no longer an overwhelmingly clear political loser for the former president, at least in a Republican primary. Mr. Trump, two months after the attack, declared the violence a “love-fest,” and has continued to do so.

Indeed, at a rally this year in Texas, Mr. Trump placed his hand on his heart and listened to the song “Justice for All” that featured his voice and those of some Jan. 6 prisoners.

Few prominent elected officials were as directly affected on Jan. 6 as former Vice President Mike Pence. But even he declined to suggest that Mr. Trump should be prosecuted and said the election should be how the matter is arbitrated.

“I believe that history will hold him to account for his actions that day,” Mr. Pence said Tuesday on NewsNation. But of an indictment, he said, “I hope it doesn’t come to that. I’m not convinced that the president acting on bad advice of a group of crank lawyers that came into the White House in the days before Jan. 6 is actually criminal.”

There were some exceptions.

The low-polling former governor of Arkansas, Asa Hutchinson, said in a statement that “Donald Trump’s actions on Jan. 6 should disqualify him from ever being president again.”

And former Gov. Chris Christie of New Jersey wrote on Twitter that he wants to see the indictment itself before offering his opinion, but added that Mr. Trump’s “conduct on January 6th proves he doesn’t care about our country & our Constitution.”

However, the details laid out in the first federal indictment against Mr. Trump — allegations that he waved material he described as secret government documents in front of people without security clearances at two of his private clubs — barely dented his support. Several Republican elected officials instinctively leaped to support him, and his poll numbers remained high or even rose.

Rob Stutzman, a Republican strategist in California who worked on Mitt Romney’s 2008 presidential race, says he believes it will eventually all become too much freight for Mr. Trump to carry to win the nomination.

“There’s been the question of electability and as these indictments pile up and details emerge, I don’t think we know yet if voters will stick with him if there appears to be viable competitive alternatives,” Mr. Stutzman said.

Mr. Trump’s team has capitalized on his past indictments to raise huge sums of campaign cash. But in Iowa on Tuesday, at a town hall-style interview with Sean Hannity of Fox News, Mr. Trump dismissed the friendly host’s suggestion that he was able to slough off his latest legal entanglement.

“No,” Mr. Trump said, “it bothers me.”

Maya King contributed reporting.