The fund-raising total would exceed previous monthly hauls and is more than double what the former vice president raised in July.

By Shane Goldmacher @ NYTimes.com, Sept. 1

Joseph R. Biden Jr. is expected to report a record-breaking haul of donations for August, raising more than $300 million between his campaign and his shared committees with the Democratic Party, according to two people familiar with the matter.

The sum would shatter past monthly records as small donors have poured money into Mr. Biden’s coffers, especially since the selection of Senator Kamala Harris as his running mate, and big contributors, from Silicon Valley to Wall Street, have given checks that can be as large as $721,300.

In a sign of the financial momentum behind Democrats, ActBlue, the main site that processes donations to the party, reported the second-biggest fund-raising day in its history on Monday, with more than $35 million donated. A majority of Mr. Biden’s August total came from online grass-roots donors, according to another person familiar with the figures.

The people familiar with Mr. Biden’s fund-raising did not know the exact final figure for the month of August, or how much higher than $300 million it would be [....]