President Trump’s campaign announced Wednesday that he had raised $24.8 million over 24 hours as he kicked off his re-election bid, an enormous haul that punctuates the financial advantage he is expected to enjoy over his Democratic challengers in 2020.

Mr. Trump’s one-day total was more than any Democratic presidential candidate raised in the entire first quarter of 2019, though it included money that went to joint fund-raising operations with the Republican National Committee. It came as he held a huge rally in Orlando, Fla., on Tuesday night, telling throngs of cheering supporters that his new campaign slogan would be “Keep America Great.”

Democratic strategists have fretted for months that Mr. Trump will spend 2019 building up a large war chest while the 23 Democrats running for president raise far smaller sums and then use that money to bludgeon one another in the primary campaign.

Mr. Trump had already raised nearly $100 million for his re-election effort by the end of March, and had more than $40 million still on hand at that time. His campaign has spent millions of dollars on online advertising on platforms like Facebook and Google to find potential small donors, an investment that appeared to pay off handsomely on Tuesday.