DES MOINES — Senator Bernie Sanders of Vermont raised more than $34.5 million in the fourth quarter of 2019, his presidential campaign said Thursday, yet another display of his enduring financial might fueled by a huge base of grass-roots donors.

Mr. Sanders received more than 1.8 million donations in the quarter, with an average donation of $18.53.

His fourth-quarter total is larger than any candidate has raised in a single quarter so far in the primary race. And it soundly eclipsed the totals of several other candidates who have reported figures for the three-month period from Oct. 1 until Dec. 31, including Pete Buttigieg, who said on Wednesday that he had raised more than $24.7 million; Joseph R. Biden Jr., who said on Thursday that he had collected $22.7 million; and Andrew Yang, who said on Thursday that he had raised more than $16.5 million.

Taken together, the high totals suggest the willingness of Democrats eager to defeat President Trump to open their checkbooks and donate to potential nominees.