Actor Robert De Niro on Tuesday spoke outside the New York court where Donald Trump is standing trial, branding him a dangerous "clown" who will become a dictator for life if reelected.

De Niro, a longtime political activist and critic of Trump, has taken a growing role in the campaign to reelect Joe Biden, including starring in a new hard-hitting TV ad for the Democratic Party.

"When Trump ran in 2016, it was like a joke," DeNiro told reporters, calling the former president a "clown" and a "tyrant."

"We have a second chance, and no one is laughing now. This is the time to stop him."

Trump has spoken daily to TV news cameras inside the court premises, claiming the trial is a political attack against him, lambasting the judge as biased and repeating falsehoods about the last election being rigged.

De Niro's unexpected press conference -- against a noisy backdrop of pro-Trump protesters and car alarms -- appeared to be an effort to push back against Trump's dominance of the TV news channels.

"If he gets in. I can tell you right now, he will never leave," De Niro said. "Is that the country we want to live in? Do we want him running this country and saying 'I'm not leaving? I'm dictator for life'?"

"The only way to preserve our freedoms and hold on to our humanity is to vote for Joe Biden for president," the legendary actor said.

He accused Trump of directing "an angry mob" to storm the US Capitol after his 2020 election defeat to Biden, adding that the Republican "ran and hid in the White House" during the violence, in which dozens of police officers were injured.

De Niro was flanked by retired officers Harry Dunn and Michael Fanone, who were wounded in the January 6, 2021 insurrection, launched to halt the certification by Congress of Biden's victory.

Dunn is one of three officers who defended the Capitol who will campaign for Biden in key battleground states ahead of the president's first election debate against Trump, slated for June 27.

They will emphasize how Trump "snapped" after losing the 2020 election, the campaign said Tuesday, pointing to his pledge to pardon the rioters on his return to office.

"Donald Trump and his unhinged quest for power and retribution pose an existential threat to our democracy," said Dunn, who bid unsuccessfully for the Democratic nomination to run for a Maryland seat in the House of Representatives.

"He continues to embrace political violence, going as far as saying there will be a 'bloodbath' if he loses again and promising to be a dictator on 'day one' and pardon January 6 rioters."

Closing arguments began Tuesday in Trump's hush money trial, less than six months before the election.