The witness list is winding down. Closing statements could come as early as Tuesday. Then a Manhattan jury will gather in the first criminal trial of a former president to determine whether Donald J. Trump will campaign this fall as a convicted felon.
The political impact of one of the most consequential jury deliberations in the nation’s history is far from predictable.
“Who knows?” said Mike Murphy, a Republican strategist who has been a longtime Trump critic. “The first casualty of the I’m-right-you’re-evil politics of today is institutional credibility. We’re not in the politics of accepting impartial facts anymore.”
But whether the verdict becomes a political turning point or not, it will be a pivotal moment in the race.
The case is the only one of Mr. Trump’s four indictments expected to come to trial and a conclusion before Election Day, even if the charges of falsifying financial records related to a hush-money payment made to a porn star do not match the gravity of the indictments accusing Mr. Trump of trying to thwart the peaceful transfer of power in 2020.
There is little doubt that Mr. Trump’s base is unlikely to abandon him now. Less clear is how swing voters or some of the traditional Democratic constituencies — younger, Black and Hispanic voters — who have expressed diminished support for Mr. Biden lately, and even flirted with Mr. Trump, would process a guilty verdict.
“We’ve looked at a lot of polling that indicates a good chunk of voters would move away from Trump if he’s convicted,” said Jim Margolis, a veteran Democratic strategist and ad maker. “I hope that turns out to be true. But if past is prologue, I don’t think we count on that happening.”
Mr. Trump’s political playbook ahead of the verdict is so worn as to be predictable.
His experience enduring multiple investigations, civil trials and two impeachments has provided a template for how he will declare victory, in the case of acquittal or a hung jury, over a deep state that was out to get him but failed. It is also the road map for how, if found guilty, he will try to undermine the legitimacy of the prosecution as a partisan sham engineered to undercut his candidacy, a message that he and allies have hammered for months.
In Trumpian shorthand, based on his previous statements, it will be a “total exoneration” if not guilty and “election interference” if convicted.
In a statement, Steven Cheung, a Trump spokesman, said Mr. Trump’s team would “fight and crush the Biden Trial Hoaxes all across the country.”
The Biden campaign has largely steered clear of speaking directly about the trial, avoiding providing any fodder to the G.O.P. claims, made without evidence, that his administration was behind the New York case. But his political operation, which declined to comment, winked at the trial last week, selling shirts after Mr. Biden proposed debates that read “Free on Wednesdays,” the weekday that the trial is paused.
But the Trump campaign, with a flair for the dramatic — and a limited travel schedule, owing to the trial — has scheduled a large rally in the Bronx on Thursday, the same day it is possible a jury could deliver a verdict, which could create a combustible situation for a country where violence has become an ugly part of the political landscape.
Mr. Trump has called some of those who face criminal charges after participating in the Jan. 6 attacks “hostages” and opened some events by playing a recording of defendants singing the national anthem from jail. Last week, the man who broke into the home of former Speaker Nancy Pelosi and bludgeoned her husband with a hammer was sentenced to 30 years in federal prison.
Bradley Beychok, co-founder of the progressive group American Bridge, which last week began what it has promised will be a $140 million anti-Trump ad campaign, said that the verdict, whatever it is, won’t change its advertising strategy.
“Democrats have to be cautious to not take the bait that our job is merely to tell voters how bad, evil and awful Donald Trump is,” he said. “He is all of those things but we have to focus on how does this affect their daily lives.”
Alex Castellanos, a veteran Republican strategist, outlined what he sees as a heads-Trump-wins, tails-Biden-loses situation as the trial comes to a conclusion.
“An acquittal would vindicate him,” he said of Mr. Trump, “and a guilty verdict would martyr him — and hey, that’s how you start religions.”
Mr. Castellanos explained Mr. Trump’s Teflon-like standing as rooted in his promise to upend institutions and institutional norms that many in the country feel have not served them well.
“He can grab women by the p-word, he can say of John McCain ‘I like heroes that haven’t been captured,’ and we all think this is the end of him, that this will hurt him,” Mr. Castellanos said. “What does history tell us? He really can shoot someone on Fifth Avenue and get away with it. Because it’s not about him. It is about who he is there to stop. The reason he can eat kryptonite is he was elected to be the hand grenade underneath the establishment’s door.”
Campaigning for the presidency under the cloud of a conviction is without precedent. One of the few prominent cases of a politician being on the ballot soon after a conviction was former Senator Ted Stevens, who lost re-election narrowly only days after he was found guilty on seven felony counts in 2008. The race was so close it was not decided until absentee ballots were counted.
Yet even as this historic trial was underway, fully 36 percent of voters said they were paying little to no attention at all, according to a recent New York Times/Siena College survey of battleground states. And crucial independent voters were even less engaged, with 45 percent saying they were paying little to no attention.
Mr. Margolis, the Democratic strategist, said the lack of television cameras in the courtroom has been the missing ingredient.
“No live TV, no video of Stormy testifying, no cut-aways of Trump sleeping,” he said of the woman, Stormy Daniels, whose sexual encounter with Mr. Trump, which he has denied, is at the center of the hush-money case. “That’s a big reason the trial hasn’t rocked America.”
The Trump campaign has been asking voters in polls what news stories they are following most and the trial has not topped 20 percent, according to a person familiar with the surveys.
Perhaps as a result, a criminal conviction could still come as a jolting surprise. The Times/Siena poll showed only 35 percent of voters in six battlegrounds saw a conviction as very or even somewhat likely.
Voters were split on whether Mr. Trump could get a fair trial in New York along predictable partisan lines, although roughly one in five Democrats thought he could not get a fair trial and about the same share of Republicans thought he could. A slim majority of independents thought he could not get a fair trial.
One political cost of the trial already been incurred for Mr. Trump: He has been confined to New York for four days a week for a month, which is significant when a candidate’s time is often considered a campaign’s most precious resource.
Mr. Murphy, the Republican strategist, said Mr. Trump’s daily courthouse remarks before the cameras — even with fawning supporters arrayed behind him — have undermined the strongman image he seeks to project.
“His brand is strength. What he likes to do is be cocky in front of an adoring crowd,” Mr. Murphy said. Instead, he said, the commentary has made Mr. Trump look more like “an old mangy lion caught in a net.”
“The whole vibe of caged, defeated animal,” he said, “is bad for Trump.”
