WASHINGTON — Democrats have traditionally trounced Republicans when it comes to raising money from small donors, but President Trump’s 2020 re-election campaign is spending heavily to try to change that.

As they prepare for a re-election fight in which grass-roots Democratic fund-raisers are expected to be particularly energized to defeat the president, Mr. Trump’s three campaign committees have spent a combined $7.9 million on digital advertising, direct mail and telemarketing — techniques used to target and cultivate low-dollar donors — over the past three months, according to campaign finance reports filed on Monday evening with the Federal Election Commission.

That was an increase in spending in those categories over the preceding quarter, and it brought the total spent on small-donor prospecting techniques by Mr. Trump’s operation to more than $39 million over the past two and a half years, putting it on pace to eclipse the $110 million it spent on those things during the 2016 presidential campaign.

At the same time, Mr. Trump has worked more assiduously to cultivate major Republican donors of the sort he disparaged his rivals for courting during his first campaign. Monday’s reports revealed six-figure donations from allies, including regulars at his private club in Palm Beach, Fla., Mar-a-Lago, and the mother of the Republican National Committee’s finance chairman.