(Reuters) - Joe Biden raised $15.2 million to support his U.S. presidential bid during the third quarter, his campaign said on Thursday, trailing some of his rivals.

U.S. Democratic presidential candidate and former U.S. Vice President Joe Biden responds to a question during a forum held by gun safety organizations the Giffords group and March For Our Lives in Las Vegas, Nevada, U.S. October 2, 2019. REUTERS/Steve Marcus

The figures, which also lag Biden’s second-quarter take of $21.5 million, come as the former vice president fights a two-front war. He faces one battle against 18 people who want the Democratic Party’s nomination and he faces another conflict with the Republican president he hopes to unseat, Donald Trump.

Other Democrats, including U.S. Senator Elizabeth Warren of Massachusetts, have chipped away at his lead in national polls and key early state nominating contests.

Trump, meanwhile, said on Thursday that both China and Ukraine should look into Biden and his businessman son Hunter, doubling down on an invitation for foreign interference in the election that had already triggered an impeachment inquiry in Congress.

Biden’s third-quarter fundraising haul lagged behind those of fellow Democratic presidential hopefuls Bernie Sanders and Pete Buttigieg, who raised $25.3 million and $19.1 million over the same period, respectively. Warren has not yet released her fundraising totals for the most recent quarter.

Trump and his party, meanwhile, jointly raised $125 million for his 2020 reelection bid in the third quarter, the Republican National Committee said on Tuesday.

Campaigns must file detailed fundraising reports for the most recent quarter to the Federal Election Commission by Oct. 15, and the numbers are closely watched to assess whether campaigns are collecting the cash needed to be competitive.

“We’ve had well over half a million contributions,” Biden told donors at a fundraiser in Palo Alto, California, on Thursday. “We haven’t raised what a lot of people have - we got started way later than everybody else - but we’ve raised, this last quarter, $15 million, in the middle of summer.”

Biden announced his candidacy in April, later than some rivals. The campaign has also abstained from accepting cash from federally registered lobbyists and certain corporate fundraising entities that are allowed raise unlimited sums of money.

Still, Biden campaign manager Greg Schultz said his candidate and their team, including over 200 staff members across the country, are in a “strong position.”

“The question any campaign faces at this point is whether or not you have the resources to compete in early states and sustain your efforts beyond,” Schultz said in a statement. “Our campaign unequivocally does and builds on our strength each week.”

Biden’s campaign said earlier on Thursday that it would spend $6 million of the $36.7 million it has raised so far on a new set of television and digital advertisements in states set to kick off the Democratic nominating contest early next February, which include Iowa, New Hampshire, South Carolina and Nevada.

Early polls show Biden likely to be a strong contender. Biden fell just two percentage points, to 18%, in the latest Sept 26-30 Reuters/Ipsos poll of Democratic-leaning voters after the House launched its impeachment probe of Trump’s dealings with Ukraine. But he has fallen 12 points in the poll since June, and Warren trails him now by just four points in the poll.