In a testament to his staying power in the Democratic presidential race, the campaign of Bernie Sanders said Thursday that he is on the verge of raising more money in March than the pace-setting $43.5 million he brought in during February.

Aides to the senator from Vermont said he has raised more than $39 million so far during March — the vast majority of it online — as the campaign touted a final-day push to top last month's figure.

Sanders's haul in February far exceeded that of Democratic front-runner Hillary Clinton, who reported bringing in $30.1 million in February. That was the second month in a row that Sanders outraised Clinton.

As part of their pitch, Sanders's aides noted the fundraising numbers they report for March will be the last before key primaries in Wisconsin and New York.

In the race for the Democratic nomination, Clinton has built a formidable lead in the delegate count. Sanders, however, has vowed to stay in the race through the party convention, saying he is capable of mounting a comeback in a series of states more favorable to him.

Last weekend, he swept caucuses in Washington state, Alaska and Hawaii.