CHARLOTTE, N.C. — President Trump inserted himself on Monday into the Democratic presidential nomination contest on the eve of its biggest day, belittling the resurgent Joseph R. Biden Jr. as a feebleminded has-been while fanning resentment among supporters of Bernie Sanders.
Traveling to one of the larger states holding a Democratic primary on Super Tuesday, Mr. Trump eagerly sought to undercut Mr. Biden at the very moment the former vice president revived his flagging campaign, taunting him for verbal gaffes and memory lapses and portraying him as an old man who even if elected would not govern but instead be committed to a retirement home.
As he has for weeks, the president likewise sought to encourage disenchantment on the left by promoting the notion that the Democratic Party establishment was trying to somehow illegitimately take away the nomination from Mr. Sanders. But Mr. Trump did not neglect the rest of the shrinking Democratic field, firing off barbs at the other candidates still in contention and even those who dropped out in the past 48 hours and threw their support to Mr. Biden.
“The Democrat party has gone crazy,” Mr. Trump said to a stadium full of cheering supporters.
The president wrapped up his rally not long before Mr. Biden’s own election-eve rally in Dallas got underway, and Mr. Trump seemed especially focused on the former vice president as a potential opponent in the fall.
He gleefully repeated recent misstatements by Mr. Biden, including his confusion over names and states, his statement that he was a candidate for the Senate, his reference to Tuesday’s primaries as “Super Thursday” and his head-spinning comment that 150 million Americans have been killed by guns since 2007.
“That means 50 percent of our country!” Mr. Trump said of the gun comment. “That’s a big story!”
“Sleepy Joe,” Mr. Trump continued, “he doesn’t even know where he is or what he’s doing or what office he’s running for. Honestly, I don’t think he knows what office he’s running for.”
If Mr. Biden won the presidency, Mr. Trump said, his staff would actually do the governing. “They’re going to put him into a home, and other people are going to be running the country,” the president said, “and they’re going to be super-left, radical crazies. And Joe’s going to be in a home and he’ll be watching television.”
A revival of Mr. Biden’s candidacy could scramble the election dynamics, giving Mr. Trump as much at stake on Tuesday as the Democrats. The president and his staff have been excited by the rise of Mr. Sanders, the Vermont senator who calls himself a democratic socialist, seeing the contrast as a favorable one in the November general election. But Mr. Trump made clear he would happily go after Mr. Biden if he emerges, too.
The rally in North Carolina was the fifth time in a row that the president has flown to a state holding a Democratic contest just before voting opened to force his way into the news cycle and try to shape the conversation. “We like to troll,” he boasted to the crowd in Charlotte.
As is often the case, the Monday night rally was more of a Trumpian stream of consciousness than a recitation of the official text sitting on the teleprompter in front of him. He accused Democrats of “trying to politicize the coronavirus” even as he focused on the politics of coronavirus and asserted that “fringe globalists” wanted to keep the borders open to infected visitors.
Mr. Trump peppered his speech with a string of false or misleading statements. “Mexico’s paying for the wall,” he insisted, even though it is not. “Yes, they are. You’ll see. You’ll see. You understand.” He boasted of preserving protections for pre-existing conditions even though his administration went to court to overturn the law guaranteeing such protections and supported legislation that would have weakened them.
As he sometimes does in these off-the-cuff riffs, he trailed off into comments that raised eyebrows. Twice at different points in his speech, he noted that he knew many parents who “don’t love their children very much.” At another point, he summoned Senator Lindsey Graham, Republican of South Carolina, to the stage and gushed over him as if he were a younger brother.
“We all have your back,” declared Mr. Graham, who lost the Republican presidential nomination to Mr. Trump in 2016, when the senator called the eventual winner a “kook” who was unfit for office. “Mr. President, you’re going to kick their ass in November.”
“Oh, my Lindsey, my Lindsey,” Mr. Trump said.
The president ridiculed the other Democratic candidates, calling former Mayor Michael R. Bloomberg of New York “a disaster waiting to happen” and “a mess,” while again mocking his would-be challenger’s height. He recalled how Senator Elizabeth Warren of Massachusetts, whom he once again mocked with a racial slur, “Pocahontas,” eviscerated Mr. Bloomberg at a recent debate. “She’s mean, she’s very mean,” he said. “She came after him and he started choking.”
Two candidates who just left the race likewise came under fire: former Mayor Pete Buttigieg of South Bend, Ind., and Senator Amy Klobuchar of Minnesota. Without any evidence, Mr. Trump contended that they made an illicit pact with Mr. Biden for their support.
“Sounds like they made a deal,” he said. “They both supported Sleepy Joe. You know why? They made a deal. You know why? Quid pro quo. That’s why.” Alluding to his own impeachment for using the power of his office to coerce campaign aid from Ukraine, Mr. Trump shouted: “Impeach them! They should be impeached! They should be impeached! Quid pro quo!”
He seemed particularly keen on fomenting discord within the Democratic Party by suggesting that the gathering support for Mr. Biden constituted a conspiracy to deny Mr. Sanders the nomination for a second election cycle in a row.
“It’s being rigged against Crazy Bernie,” Mr. Trump said. “Crazy Bernie’s going to go crazy, crazy.”
Maggie Haberman reported from Charlotte, and Peter Baker from Washington.