Joe Biden sought to turn Donald Trump’s impeachment to his own advantage at the fifth Democrat presidential debate, declaring it showed he was the candidate the president feared most.
Mr Biden told the audience in Atlanta: "I’ve learned something from these impeachment trials – I’ve learned, number one, that Donald Trump doesn’t want me to be the nominee. Secondly, I found out Vladimir Putin doesn’t want me to be president."
The former vice president, who is no longer the clear frontrunner in polls, spoke on a day when a key witness told the impeachment inquiry Mr Trump had authorised a "quid pro quo" in an attempt to get the government of Ukraine to investigate Mr Biden.
Asked if, as president, he would pursue a prosecution against an ex-president Trump, Mr Biden said: "I would not direct it, and I don’t think it’s a good idea that we mock, that we model ourselves after Trump and say ‘Lock him up,’" he said.
Mr Biden’s performance was regarded as his strongest so far but was undermined by a late gaffe.
He touted how he had been supported by the "only" black female US senator. Mr Biden appeared to momentarily forget that the second black woman elected to the Senate, Kamala Harris, was standing with him on the debate stage.
Other candidates united with Mr Biden in backing the impeachment inquiry.
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Elizabeth Warren said she had already decided to convict Mr Trump in a Senate trial. She added: "We have to establish the principle that no one is above the law."
Ms Harris said there was a "criminal in the White House" and Bernie Sanders called the president a "pathological liar."
However, they once again argued over how to expand healthcare coverage for Americans, and Mrs Warren’s proposed "wealth tax" on billionaires.
Pete Buttigieg, the young small town mayor, who recently shot into the lead in a poll in the early voting state of Iowa, was attacked by several other candidates for a lack of experience.
Senator Amy Klobuchar, the author of a vast number of bills in Congress, referred to him as a "local official".
Mr Buttigieg responded that "Washington experience isn’t the only experience."
He added: "I know that from the perspective of Washington what goes on in my city might look small. But frankly, where we live, the infighting on Capitol Hill is what looks small."
The Democratic debate came just 11 weeks before the first contest in Iowa on Feb. 3, raising the stakes for the 10 participants.
The race recently appeared to crystalise into a a three-way battle between the moderate Mr Biden, and Mrs Warren and Mr Sanders on the left.
Mrs Warren has seen some of her momentum fade over how she would pay for her government-run healthcare plan.
Mr Biden said the "vast majority" of Democrats did not support it, and it could not be passed in Congress
But Mr Sanders said: "Some of the people up here think we should not take on the insurance industry. I think now is the time."
A clash erupted between two candidates with relatively low polling who were looking for big moments.
Ms Harris attacked congresswoman Tulsi Gabbard, who has criticised prominent Democrats including Hillary Clinton.
"I think that it’s unfortunate that we have someone on the stage who is attempting to be the Democratic who during the Obama administration spent four years full time on Fox News criticising President Obama," Ms Harris said.
Ms Gabbard responded that she was "not going to put party interests first" over those of America.