Vice president Kamala Harris and Gavin Newsom, the governor of California,are among those being considered to replace Joe Biden should the 81-year-old stand aside in the US presidential election after his latest Nato summit gaffe. 

The president referred to Volodymyr Zelensky as “President Putin” and Kamala Harris as “Vice President Trump” in a pair of significant gaffes that worsened the crisis engulfing his presidency.

The blunder followed Biden’s shaky performance in the first US presidential debate of the 2024 election, in which froze, stuttered and lost his train of thought on stage. 

Mr Newsom, 56, was mobbed by reporters after the debate ended, with many asking if he would step in for the ailing president who rambled in response to questions from Donald Trump. 

Mr Newsom, who has the best odds to win the 2024 election of any alternative candidate, attempted to swat aside the question, saying the rumours were “unhelpful” and “unnecessary”.

But advisers close to three potential replacements for Mr Biden – thought to include Mr Newsom – said they were bombarded with pleas for their employers to step-up as an alternative, according to Politico.

“Biden needs to drop out. No question about it,” one said.

At 56, Mr Newsom is a quarter of a century younger than Mr Biden and an adept communicator, who runs the world’s fifth-largest economy.

He was re-elected to his second and final term as governor of California in a landslide victory in 2022.

With no political threats to fend off in the Golden State, he has focused on increasing his national recognition, giving speeches in other states, and running national TV adverts.

He has amplified his political profile by wading into this year’s White House race, casting himself as an attack dog who is prepared to aggressively take on prominent Republicans.

His strategy included challenging Ron DeSantis, Florida’s governor and one-time GOP 2024 presidential candidate, to a debate.

The actions caused some unease in the White House, where aides feared he could launch a challenge against Mr Biden, although he publicly and privately assured the president otherwise.

Mr Newsom has tacked to the Left of the Democrat party, which may dampen appeal among centrist voters who backed Mr Biden in 2020.

He has enacted more than a dozen laws aimed at making California a sanctuary for women seeking abortions in states where the procedure is now banned.

Mr Newsom has also championed green policies, ordering a ban on the sale of new fossil-fuel cars by 2035.

And he has looked to ease obstacles for illegal immigrants, making California the first state to offer health insurance for all undocumented immigrants.

Gretchen Whitmer, 52, secured a convincing victory in the swing state of Michigan in 2020.

Like Mr Newsom, Ms Whitmer is a rising star of the Democratic party who tends to be sought out by American news networks sniffing out possible future presidents.

Mr Biden considered her as a running mate in 2020 – she was reportedly one of four who made the all-female shortlist before Kamala Harris was selected – and she has publicly clashed with Donald Trump before.

She shot down speculation last year about a presidential bid, saying she wanted to see out her second term as governor and supported Mr Biden. But she has hinted at running at the next election in 2029.

She successfully turned an insult from Mr Trump – “that woman in Michigan” – into a slogan that raised her national profile.

Her personal brand is connected with the abortion debate: she has accused Donald Trump of lying about his stance on reproductive rights (she suspects he would seek a national ban on abortion), and won her won reelection in 2022 against a Trump-endorsed opponent, Tudor Dixon, who was considered to be at the extreme end of the anti-abortion right.

That victory – she came home by a handy 11 percentage points, a much more than polls predicted – will only add to her allure for Democrats looking for a candidate who can take on the right.

Another name mentioned is Sherrod Brown, the last Democrat senator in Republican voting state of Ohio.

A career politician and at 71, he is one of a small clutch of “Red State Democrats” who owe their political success to a strong personal brand and local issues.

Mr Brown’s brand is messy hair, a rumpled suit and a working man persona. He is an ally of Bernie Sanders and considered one of the most liberal figures in the Democrat party – which is one reason he is sometimes suggested as someone who could unify the party’s establishment and progressive wings.

He was considered as a running mate for Hillary Clinton in her 2016 presidential run.

Mr Beshear’s potential appeal to the Democrats can be summed up in the headline of a recent Wall Street Journal profile of him:  “This Democratic Governor Knows How to Win in a Red State. Is His Party Listening?”

He has twice won the governorship in a determinedly Red State. He’s rated as the most popular Democratic governor in the country, and his name has come up as a potential presidential candidate since he first took office in 2019. Like many of the others mentioned as a possible replacement for Biden, he is thought to be considering a run in 2028.

In America’s ultra-polarised political climate, a Democrat who can reach across the political divide to Republican voters would be a massive asset. His political brand - which boils down to a mild mannered demeanor and expressing compassion for all - does well in his home state.

But not everyone is convinced his appeal is transferable. At home he has the advantage of a local political dynasty - his father was also Kentucky state governor - and the bond he forged with Kentuckians during Covid and a series of natural disasters in the state may be difficult to replicate nationally.

And would a Democrat party dominated by liberal coastal cities be ready to nominate a southern White man?

The most obvious option in establishment Democrat circles is of course vice-president Kamala Harris.

However, she polls worse than Mr Biden and may be sunk by her close work with the president.

Members of Mr Biden’s cabinet, including transportation secretary Pete Buttigieg and commerce secretary Gina Raimondo, are also considered viable contenders.

Nevertheless, Democrats who are intimately acquainted with Mr Biden insist there is little that can be done to dissuade him from seeking a second term.

Insiders suggest the two voices the president plays closest attention to – his wife Jill and his sister Valerie – remain staunchly supportive of his re-election bid.

David Axelrod, a former chief strategist for Barack Obama, told CNN: “The idea he would walk away from this is pretty remote. But his job got harder tonight.”