Biden running mate news triggers "best grassroots fundraising day ever"

More than $10.8 million was donated in four hours after Sen. Kamala Harris was announced as presumptive Democratic presidential nominee Joe Biden's running mate Tuesday, the Democrats' main donation-processing platform ActBlue said, per the New York Times.

Why it matters: Biden is lagging behind in fundraising to President Trump, whose campaign and the Republican National Committee out-raised that of the Democrats' last month. But Biden's announcement triggered his campaign's "best fund-raising hour," his deputy digital director, Clarke Humphrey tweeted, adding it was the campaign's "best grassroots fundraising day ever." ActBlue took $2.3 million in donations during the same hours of 4pm to 8pm Monday, "suggesting a bump as large as $8.5 million" for Biden, the Times notes.

Go deeper: Political world reacts to Biden tapping Kamala Harris as running mate