The start of Donald J. Trump’s criminal trial on Monday thrusts the 2024 presidential race into uncharted territory and Mr. Trump back into the public spotlight in ways he hasn’t been since he left the White House more than three years ago.

There will be no cameras in the Manhattan courtroom. But Mr. Trump and the drama around him may be unavoidable as he goes on trial in a case that centers on a salacious hush-money payment made to a porn star in the run-up to the 2016 election and that threatens the presumptive Republican nominee with potential jail time for 34 felony counts.

The trial will begin with perhaps the most scrutinized jury selection since the trial of O.J. Simpson three decades ago, and it will confine Mr. Trump to New York City for as many as four days a week for about eight weeks, and possibly more.

That would be roughly one-quarter of the calendar until the November election.

“This looks like no other presidential campaign in the history of the country,” said Neil Newhouse, a Republican pollster who has worked on past presidential races. “It kind of puts the regular presidential campaign on sabbatical.”

Mr. Trump has told advisers he wants as much media coverage of his court appearances as possible and many supporters defending him on television, as the gravitational center of the campaign shifts away from the battleground states to a courtroom in Lower Manhattan. And he has deliberately created a circuslike atmosphere around his previous criminal arraignments, including by going straight from a Miami courthouse to a popular Cuban restaurant and, at his New York legal proceedings, by holding news conferences at his property at 40 Wall Street. He is likely to repeat that approach, according to an adviser.

“On Monday all hell breaks loose!” Mr. Trump wrote to supporters on Friday in a fund-raising email, asking for “peaceful patriotic support.”

He is expected to hold events around New York City, in parts of the boroughs outside of Manhattan that are more politically hospitable to him on days when he is not in court, and possibly on the evenings of those when he is. Day trips to battlegrounds for rallies are possible on Wednesdays, when the trial is scheduled to pause weekly, with advisers noting that Mr. Trump has a private plane.

Jury selection is scheduled to begin on Monday, with questionnaires probing prospective jurors’ opinions of Mr. Trump, what podcasts they listen to and even what news outlets they consume, as he sits in the courtroom, watching.

The case will also be a test for how the news media handles multiple days of potentially fast-moving developments around Mr. Trump. In one recent MSNBC segment, Michael Avenatti, the media-hungry attorney who once represented the porn star in the case, dialed in live from prison, where he is serving time on unrelated charges. Among the questions for people who program television: If Mr. Trump chooses to narrate the day’s developments in news conferences, will the networks carry it live?

President Biden and his campaign have taken a virtual vow of silence about the trial, seeing any remarks as potentially feeding Mr. Trump’s claims that this case and his three other indictments are part of a broader “election interference” scheme (there is no evidence that the White House played any role in his indictments in New York and elsewhere). But Biden advisers say they hope the trial will amplify their argument that the former president is running chiefly to help himself, including to stay out of prison.

The Biden and Trump campaigns both declined to comment.

The sheer focus on Mr. Trump and one of his criminal indictments could prove helpful for a Biden team that is pressing to make the 2024 contest as much about the predecessor as the president.

“Here’s the fundamental Trump messaging task right now,” said Pat Dennis, the president of a Democratic super PAC, American Bridge 21st Century, that is planning to track the trial closely. “He has benefited from being outside the spotlight and we need to remind people what this guy was like, why voters were so sick of him.”

Whit Ayres, a Republican pollster, said the closest parallel would be the televised Jan. 6 congressional hearings of 2022 that drew nationwide attention — and that Republicans proudly tuned out and Democrats obsessed over.

A poll by The New York Times and Siena College just ahead of the trial showed that 58 percent of voters — and 54 percent of independents — viewed the charges as very or somewhat serious. But nearly one in five voters said they were unsure if he should be found guilty. Some public polling has shown that a small but significant bloc of voters could be swayed by a conviction.

Even some of Mr. Trump’s critics, both inside the Republican Party and among Democrats, have expressed worry that the Manhattan case is coming first, and could be the only trial held before the election. The concern is in part because Alvin L. Bragg, the Manhattan district attorney who brought the charges, is an elected Democrat, unlike the Justice Department’s special counsel, Jack Smith. But it is also because the accusations themselves are less sweeping and fundamental than the charges that Mr. Trump tried to thwart the peaceful transfer of power.

Of course, Mr. Trump himself could make a zoo of the proceedings. He will be compelled to sit and listen to Stormy Daniels, the former adult film star who has said she had a sexual relationship with him; Michael Cohen, his former fixer; and aides who worked closely with him testify about the affair and the resulting payment.

Mr. Trump has already showed little patience as a courtroom attendee, storming out of the court in the closing arguments of the E. Jean Carroll sexual abuse and defamation case and earning rebukes from the judge. A jury ultimately ordered Mr. Trump to pay more than $83 million to Ms. Carroll for defaming her after she accused him of rape.

“The X factor — I will call this a known unknown — he’s going to lose his mind,” said Anna Greenberg, a Democratic pollster.

Mr. Trump’s lawyers have warned him repeatedly that he needs to try not to behave erratically in front of juries and that some judges will have him put in jail if he does.

An array of conservative activists with close ties to Mr. Trump and those in his orbit are planning trips to New York for daily protests and media appearances. The New York Young Republican Club plans to stage pro-Trump rallies in Collect Pond Park near the courthouse, according to the group’s executive secretary, Vish Burra, who said in an interview he had been coordinating with the New York Police Department on logistics.

Other Trump allies, such as the right-wing activist Laura Loomer, will be in New York to broadcast pro-Trump messages and attack the judge overseeing the case, Justice Juan M. Merchan, and the judge’s daughter, who has consulted for Democrats. Mr. Trump’s former chief strategist, Stephen K. Bannon, whose “War Room” podcast has a huge following among hard-line activists, will have correspondents, including Ms. Loomer, on the scene.

Ms. Loomer does not work for Mr. Trump but she has flown with him on his plane and met with him at his private clubs. He frequently encourages her attacks against his perceived enemies, including her online posting about Justice Merchan’s daughter.

“We have to raise awareness about this banana republic witch hunt against President Trump,” Ms. Loomer said in an interview. “I will have my bullhorn. I will have my camera crew. I will have my Trump gear and I will have a staff writer.”

Mike Davis, a lawyer and Trump ally who is expected to appear with Ms. Loomer on Mr. Bannon’s show, said, “When judges and prosecutors enter the political ring, they should expect political punches.”

Even before the trial, Mr. Trump has almost dared Justice Merchan to sanction him. In early April, the judge expanded his gag order to prevent the former president from attacking not just witnesses, prosecutors, jurors and court staff but also relatives of the judge and Mr. Bragg. Over the weekend, Mr. Trump attacked Mr. Cohen on social media.

Mr. Trump has accused the judge of violating the Constitution with his gag order. “If this Partisan Hack wants to put me in the ‘clink’ for speaking the open and obvious TRUTH, I will gladly become a Modern Day Nelson Mandela,” Mr. Trump wrote on his social media site, comparing himself to the anti-apartheid activist in South Africa.

In the Republican primary, Mr. Trump repeatedly showed he could turn his legal jeopardy into political advantage. His strongest fund-raising day was when his mug shot was taken when he was booked in Atlanta. Donations similarly surged when he was first indicted in New York.

It is less clear what his claims of victimhood will do in a general election, with polling showing some swing voters declining to vote for Mr. Trump if he is convicted.

Mr. Biden has not engaged publicly with the case’s specifics. But his advisers are setting up a schedule for him to be in battleground states, sharpening the contrast with the courtroom-confined Mr. Trump. Mr. Biden will hold five events over a three-day stretch in Pennsylvania this week as jury selection begins.