President Trump speaks to supporters during a rally on March 2, 2020, in Charlotte, North Carolina. Getty

President Trump gloated about the stock market roaring back Monday, while throwing sharp barbs at the thinning Democratic presidential field on the eve of Super Tuesday's big round of primaries.

Mr. Trump's spirits were high after the Dow Jones Industrial Average soared nearly 1,300 points, or 5%, clawing back from a seven-day rout in which it dropped more than 3,500 points. Stocks rose Monday on hopes that central banks will take action to shield the global economy from the effects of the coronavirus outbreak.

"Do you think our opponents were thrilled when they saw the stock market today?" asked Mr. Trump, who has taken credit for a bull market throughout his three years in office.

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The president threw some of his hardest punches at former Vice President Joe Biden, who is coming off a decisive win in Saturday's South Carolina primary. Mr. Trump picked at Biden's propensity for rhetorical stumbles on the stump, suggesting it was a sign of senility.

"I honestly don't think he knows what office he's running for," Mr. Trump said. He added: "He's not going to be running it. Other people are going to be running it. ... They're going to be super left radicals, Joe is going to be in a home watching television."

Mr. Trump allowed that Vermont Senator Bernie Sanders, who finished at or near the top in three of the first four nominating contests, "does have some enthusiasm, but much less than we have."

It's a crucial moment in the nomination battle: Biden is making the case that moderates need to consolidate behind him to stop Sanders, a Democratic socialist, and give Democrats a shot at beating Mr. Trump in November.

Two moderates have exited the race: former South Bend, Indiana, Mayor Pete Buttigieg and Minnesota Senator Amy Klobuchar. Former New York City Mayor Michael Bloomberg, who skipped the first four contests, will appear on the ballot for the first time Tuesday.

Mr. Trump speculated there may have been a "quid pro quo" for Buttigieg — the offer of a job in the next Democratic administration for dropping out and endorsing Biden.

"Impeach them. They should be impeached," Mr. Trump said.

Mr. Trump has offered daily commentary on the Democratic race, alternately boasting that no Democrat has a chance against him, ridiculing the top tier of candidates with derisive nicknames, and arguing that the party's establishment is trying to steal the nomination from Sanders.

Sanders shot back at Mr. Trump on CNN on Monday night, saying: "President Trump, stay out of the Democratic primary. Why don't you do your job for a change as president?"

Earlier Monday, Mr. Trump said he had no qualms about attending a large stadium rally despite the coronavirus threat.

"I think it's very safe," Mr. Trump said of campaign rallies, adding that the Democratic candidates are having plenty of rallies themselves.

The threat of the virus didn't deter fans of Mr. Trump from attending Monday's rally in Charlotte, where people in the stands shared buckets of chicken fingers and dunked their hands into shared vats of popcorn while they awaited the president's arrival.

The coronavirus outbreak has killed more than 3,000 globally and upended life for many around the globe. In the U.S., the number of infections has surpassed 100, with six dead. Federal officials have not advised against large gatherings in the U.S., leaving that to local officials to address.

North Carolina, a perennial swing state, is among the 14 states, one territory and voters abroad that will cast their ballots Tuesday, races that represent about a third of all delegates.

Mr. Trump's rally in Charlotte follows his campaign's pattern of churning out robust counter-programming throughout the Democratic nominating process. In recent weeks, the president has held rallies in each of the four early voting states for the presidential nomination.

The president and the GOP are giving North Carolina, which has been decided by close margins over the last three presidential election cycles, plenty of attention.

Republicans have picked Charlotte to host the Republican National Convention. Mr. Trump also visited Charlotte last month as part of a series of revitalization and "opportunity now" summits, programs he and administration officials have highlighted as he tries to chip away at the Democrats' electoral advantage in minority communities.