Democratic U.S. presidential candidate and former Vice President Joe Biden reacts during a campaign stop in Los Angeles, California, U.S., March 4, 2020. REUTERS/Mike Blake

WASHINGTON (Reuters) - Former Vice President Joe Biden’s presidential campaign raised $7.1 million in online donations in 42 hours, his campaign said late on Wednesday, a boost in fundraising for a candidate who has struggled to keep pace with his rivals and has been vastly outspent by fellow frontrunner Bernie Sanders.

Sanders’ campaign disclosed on Tuesday in a that in a two-day window the U.S. senator had raised $5.5 million from more than 220,000 donations.

The two men are locked in a tight race to secure the Democratic nomination for president and the opportunity to challenge Republican President Donald Trump in November.