Joe Biden has said President Donald Trump's refusal to concede defeat in last week's White House election is "an embarrassment".
But the US president-elect - who has been making contact with foreign leaders - insisted nothing would stop the transfer of power, reports BBC.
Mr Trump meanwhile tweeted he would ultimately win the race that all major TV networks have forecast he lost.
As happens every four years, US media projected the election victor.
None of the state-by-state results have yet been certified, several vote counts are continuing, and the outcome will only be set in stone once the US Electoral College meets on 14 December.
What did Biden say?
The president-elect was asked by a reporter on Tuesday what he thought of President Trump's refusal to acknowledge defeat.
"I just think it's an embarrassment, quite frankly," Mr Biden, a Democrat, said in Wilmington, Delaware.
"The only thing that, how can I say this tactfully, I think it will not help the president's legacy."
"At the end of the day, you know, it's all going to come to fruition on January 20," he added, referring to inauguration day.
Mr Biden has been fielding phone calls with foreign leaders as he prepares to assume office.
UK Prime Minister Boris Johnson, Irish Taoiseach Micheál Martin, French President Emmanuel Macron and German Chancellor Angela Merkel were among those he spoke to on Tuesday.
Referring to those calls, Mr Biden said: "I'm letting them know that America is back. We're going to be back in the game."
He and Vice President-elect Kamala Harris are forging ahead with the transition. But a little-known government agency led by a Trump appointee is stalling the handover.
The General Services Administration co-ordinates funding and access to federal departments for incoming administrations. However, it has so far declined to formally recognise Mr Biden as president-elect.
Nevertheless, the president-elect said: "We don't see anything slowing us down, quite frankly."
What did Trump and his allies say?
On Tuesday, Mr Trump took to Twitter to fire off several tweets in capital letters about "massive ballot counting abuse," asserting: "We will win!"
His tweets were labelled by the social media network as disputed.
The president has been making unsubstantiated claims that Mr Biden was only able to win the election through electoral corruption, but no evidence has emerged so far to support the allegation.
US Secretary of State Mike Pompeo, a Trump loyalist, told a news conference at the Department of State on Tuesday that once every "legal" vote was counted a "second Trump administration" would begin.
Mr Trump's fellow Republicans have largely refrained from acknowledging Mr Biden's projected victory.
Asked on Tuesday why he had not congratulated the Democrat, Senator Ron Johnson of Wisconsin said: "Nothing to congratulate him about."
Missouri Senator Roy Blunt said Mr Trump "may not have been defeated at all".
Senate Republican leader Mitch McConnell has said Mr Trump has every right to launch legal challenges to the result in several battleground states such as Pennsylvania.
What's happening with Senate races?
Republicans received a boost on Tuesday in their campaign to keep control of the upper chamber of Congress as a Democratic challenger conceded defeat in a North Carolina race.
The state's Republican incumbent Thom Tillis narrowly held on after his Democratic opponent, Cal Cunningham, was engulfed by scandal over an extramarital affair.
With North Carolina settled, all eyes will now turn to Georgia, where the two senate seats currently held by Republicans will be decided in a runoff election in January.
If the Democrats win both seats - which won't be easy - they could still flip control of the Senate. That's because, in the event of a 50-50 tie, the vice-president is the tie-breaker, and Kamala Harris is due to take office in January.
Last week, Republicans were also able to retake an Alabama Senate seat won by Democrats in 2018, though they lost seats in Colorado and Arizona. The Republican candidate is currently leading in Alaska's race, where votes are still being tabulated.