White House hopeful Joe Biden doubled down on his vow to cooperate with Republicans should he be elected president, saying he successfully worked across the aisle as vice president.

"There's an awful lot of really good Republicans out there," he said Saturday at a Massachusetts fundraiser. "I get in trouble for saying that with Democrats, but the truth of the matter is, every time we ever got in trouble with our administration, remember who got sent up to Capitol Hill to fix it? Me. Because they know I respect the other team."

Biden added that many conservatives are being "intimidated" to follow in lockstep with President Trump.

"They're decent people. They ran because they care about things, but they're intimidated right now," he told the fundraiser's attendees.

Similar comments have in the past infuriated progressive activists, who are in search for a candidate who can effectively fight against Trump and the GOP's agenda and argue that the former vice president is naïve to suggest Republicans on Capitol Hill are interested in bipartisanship.

But, Biden, who leveraged his decades serving in the Senate to help become one of the Obama administration's chief negotiators on Capitol Hill, has maintained that reaching across the aisle is the only way to implement long-lasting change.

"If you start off with the notion there's nothing you can do, well why don't you all go home then, man? Or let's start a real physical revolution if you're talking about it. Because we have to be able to change what we're doing within our system," Biden said in June.

"You have to go out and beat these folks if they don't agree with you, by making your case - and that's what presidents are supposed to do: Persuade the public. Move people as to what's going on."

Despite liberal pushback toward his bipartisan strategy, Biden has maintained his leads in most national and statewide primary polls ahead of several other frontrunners, including Sens. Elizabeth Warren (D-Mass.), Bernie Sanders (I-Vt.) and Kamala Harris (D-Calif.), all of whom are seeking to angle their campaigns' appeal to the Democrats' progressive flank.

--This report was updated on Aug. 18 at 7:48 a.m.