Senator Chris Coons, who is tipped to be Biden’s secretary of state, said the prime minister’s comments about Obama during the Brexit referendum campaign were “not well received”.
The Democrat politician also suggested Johnson may have “copied” Donald Trump’s style but stressed that he found the PM to be more “agile, engaging, educated and forward-looking” than his caricature in the US press.
In comments dubbed “foolish” by Labour on Sunday, Johnson suggested in April 2016 that Obama’s “part-Kenyan heritage” meant he had an “ancestral dislike of the British empire” that had led him to remove a bust of Winston Churchill from the White House’s Oval Office.
It came as Obama intervened in the Brexit referendum debate, during which Johnson led the Leave campaign, to urge the UK to “stick together” with the EU.
Coons said the Biden and Johnson administrations would “share a number of priorities” including tackling climate change, privacy issues and promoting democracy.
But discussing Johnson’s potential relationship with Biden, who was vice president under Obama at the time of the part-Kenyan comments, Coons told BBC One’s Andrew Marr Show:
“The special relationship between the United states and the United Kingdom has endured over decades and I expect there will be opportunities promptly for there to be some visits and conversations and some reconsideration of whatever comments may have been made about the moment of Brexit.”
Asked directly about Johnson’s comments, Coons said: “That certainly wasn’t one that was well received on my part.
“But frankly rather than relitigating or revisiting comments that may have been made days or years ago I think as we reimagine our engagement with our vital allies around the world, it’s important in a post-Trump era to have an open mind about how we can work together, especially with nations as important to the United States as the United Kingdom.”
Coons also signalled Biden was willing to continue talks on a UK-US trade deal but warned that the Irish heritage president-elect had “significant concerns” about Brexit’s impact on the Good Friday Agreement for peace in Northern Ireland.
He said: “There are of course significant concerns here about how any departure arrangements or final status between the UK and EU might impact the border in Northern Ireland.
“There’s obviously agricultural concerns, I’m from a state known for its chicken exports.
“But with close allies, whether it’s Canada or Mexico, Germany or the UK, we always have points of pressure and tension with trade that need to be worked out in the way that friends do in an open-handed and fair-minded way.”
Foreign secretary Dominic Raab meanwhile dismissed concerns about Biden’s past criticism of Johnson while noting that the president’s elect’s “interest” in peace in Northern Ireland would not “in any way dim”.
He told Marr: ″We’re two years on from that and I thought it was very interesting hearing from Senator Coons that he’s not interested, and he doesn’t think that the administration are going to be interested in relitigating old issues, not least as we’ve left the EU, we leave the transition period by the time the inauguration happens.
“What he’s looking for, what the Americans will be looking for, I’m sure, is the opportunities of the future.”
Shadow justice secretary David Lammy meanwhile highlighted the opposition's links with Biden, describing Labour and the Democrats as "sister parties" and highlighting his own friendship with Obama and conversations with senior senator Patrick Leahy.
Lammy also suggested Johnson's past conduct may cause difficulties for his relationship with Biden.
He told Marr: "It was foolish of Boris Johnson to put the Good Friday Agreement on t he table in t he way that he did when you know you've got an Irish-American who might become leader of his country and where the Democrats had longstanding concerns.
"It was foolish to insult Barack Obama, foolish to insult Hillary Clinton, all of those things I have reflected on and discussed with our Democratic colleagues."