The former vice-president, who is leading the race to become the 2020 Democratic nominee, made the remark at a fundraiser on Monday night, according to a Daily Beast reporter.
“With Trump gone you’re going to begin to see things change,” Mr Biden reportedly said. “Because these folks know better. They know this isn’t what they’re supposed to be doing.”
The comment came at the end of what was considered a damaging week on the campaign trail, after the 76-year-old appeared to flip-flop on federal funding for abortion and was attacked by rivals for pushing “the same old politics”.
“Biden's delusion that somehow Trump is the only problem with the Republicans is disqualifying,” tweeted David Rothkopf, a prominent political scientist who supports the Democratic Party.
“It shows either a faulty memory, a gross analytical failure, wishful thinking or a willingness to lie in order to make his ‘bridge-building’ candidacy seem more plausible.”
Critics pointed out a number of moves by Senate majority leader Mitch McConnell to block Democratic priorities before Mr Trump was ever on the scene.
These included repeated attempts to block almost any form of gun-control legislation, as well as Mr McConnell’s unprecedented refusal in 2016 to hold a vote on president Barack Obama’s supreme court nominee Merrick Garland.
Dante Atkins, a former aide to Democratic congressman John Garamendi, called Mr Biden “completely oblivious to the current state of our politics”, while former deputy chief of staff to senator Harry Reid, Adam Jentleson, tweeted he was “living in the past”.
Jonathan Lipman, who served as Democratic senator Jeanne Shaheen’s communications chief, tweeted: “He is ultimately a creature of the bygone era of Senate conviviality. That was his political life for 40 years. He literally can't help but believe it.”
At the Iowa Democratic Party’s annual summer fundraiser in Cedar Rapids on Sunday, rivals Bernie Sanders, Pete Buttigieg and Kirsten Gillibrand all used their five-minute speech before party officials to attack Mr Biden.
Mr Sanders, who is among the most progressive of the candidates, claimed the “same old politics will not” defeat Mr Trump in 2020.
“I understand there are some well-intentioned Democrats and candidates who believe the best way forward is a middle-ground strategy that antagonises no one, that stands up to nobody and that changes nothing,” he said.
“In my view, that approach is not just bad public policy, but it is a failed political strategy.”
Mr Buttigieg, the mayor South Bend, Indiana, mocked the idea of Democrats returning to views the party held in the 1990s.
“We’re not going to win by playing it safe or promising a return to normal,” he said.
Ms Gillibrand, senator for New York, said: “Now is not the time to be polite. Now is not the time for small steps."