Trump is behind "incredibly damaging messages being sent to the rest of the world about how democracy functions," Biden told reporters in his home state of Delaware.
Asked about Trump's calls with officials in Michigan, which Biden won on November 3 election by 155,000 votes, Biden said it was "another incident where he will go down in history as being one of the most irresponsible presidents in American history."
"It's hard to fathom how this man thinks," Biden said. "I'm confident he knows he hasn't won, is not going to be able to win and we're going to be sworn in January 20th."
Trump has refused to accept his loss on November 3, despite his opponent getting over six million more votes.
Biden also won the Electoral College votes that ultimately decide who takes the White House by 306 to 232, flipping five states that went to Trump four years ago.
After initially making baseless claims of widespread fraud, Trump has appeared to shift his strategy to asking states to overrule the will of voters.
In Michigan, Trump placed a telephone call to a Republican on a once-obscure board who wants to withdraw her certification of the election result in the heavily Democratic county that includes majority-Black Detroit.
"He was checking to make sure I was safe after seeing/hearing about the threats and doxxing," Wayne County Board of Canvassers chairwoman Monica Palmer told the Detroit Free Press, referring to personal information posted about her on social media.
Trump also reportedly invited Michigan Republican lawmakers to the White House, even as his campaign withdrew a federal lawsuit that asked the courts to block final certification of the state's results.
Biden's margin of victory in Michigan is more than 10 times higher than Trump's when he won the state in 2016.
More accusations by Trump camp
Georgia is preparing to release results of a hand recount of its five million ballots that is expected to show that Biden is the first Democratic presidential candidate to win the southern state in almost three decades.
Trump dispatched his lawyer Rudy Giuliani to give a news conference Thursday where he read affidavits claiming fraudulent voter activity in multiple states and said the campaign would file a new lawsuit in Georgia.
Giuliani, a former mayor of New York, also brazenly accused Democrats of being "crooks" who committed massive fraud in several battleground states "to steal an election from the American people."
"It changes the results of the election in Michigan if you take out Wayne County," said Giuliani, who repeatedly wiped sweat from his brow and at one point had a dark liquid which may or may not have been hair dye snaking down the side of his face.
As Giuliani and other Trump lawyers outlined claims that included charges of communist involvement, the president -- apparently watching on television -- took to Twitter to applaud them for laying out "an open-and-shut case of voter fraud."
Chris Krebs, the top US election security official who was fired by Trump after calling the election the most secure ever, wrote on Twitter that the news conference was "the most dangerous 1hr 45 minutes of television in American history" and "possibly the craziest."
Recount 'did its job'
In Georgia, Biden's original winning margin was just over 14,000 votes.
The hand recount that began last week and concluded late Wednesday narrowed that gap slightly to more than 12,700 as of early Thursday.
Some discrepancies were found in Republican leaning counties, according to Gabriel Sterling, Georgia's voting system manager who helped monitor the so-called risk-level audit.
"The good part was, the audit did its job. It found those tranches of votes," he told Fox News.
The issues, which were chalked up to human error and not fraud, included memory cards that were not scanned in Douglas and Walton counties, more than 2,700 missing votes in Fayette County, and 2,600 ballots from Floyd County that were not scanned.
Georgia's Secretary of State Brad Raffensperger, who like Sterling is a Republican, said there was no widespread voter fraud.
"I don't believe at the end of the day it'll change the total results," Raffensperger told CNN.
The laser-like focus on Georgia is not just because of the recount. The state's two US Senate races are going to runoffs on January 5 that will determine control of the chamber and Biden's ability to push through his agenda.
