Actor Robert De Niro has launched a spray at “two-bit big shot” Donald Trump outside the court where Republican presidential candidate’s hush money trial is winding up.

De Niro, a long-time Democrat who recently voiced an ad for US President Joe Biden, unleashed at a surprise Biden presidential campaign event on Tuesday outside the Manhattan courtroom where Trump’s trial is coming to an end.

Oscar winner De Niro turned up to the press conference with two former law enforcement officers, Harry Dunn and Michael Fanone. Both were at the US Capitol when it was attacked by Trump supporters on January 6, 2021.

“We’ve forgotten the lessons of history that showed us other clowns who weren’t taken seriously until they became vicious dictators,” De Niro said in comments broadcast widely by US media, including Fox News.

He said Trump’s run for US president in 2016 was initially laughed off as a joke.

“With Trump we have a second chance and no one is laughing now. This is the time to stop him by voting him out once and for all,” he said.

The remarks were part of the Biden campaign’s attempt to use wall-to-wall media coverage of the Trump trial to push their own message: Trump is a danger to democracy.

De Niro warned that Americans could see civil liberties they take for granted evaporate if Trump is returned to the White House later this year – as well as the end of elections.

“I don’t mean to scare you. No, no wait, maybe I do mean to scare you,” he said.

“If Trump returns to the White House, you can kiss away these freedoms that we take for granted – and elections, forget about it … He will never leave.”

Fanone and Dunn delivered emotional remarks, saying violence at the Capitol was fuelled by Trump’s lies that the 2020 election was stolen.

They and De Niro were heckled by a Trump supporter as pro-Trump demonstrators chanted in the background.

Trump campaign officials dismissed the De Niro event as a stunt, saying it showed desperation in the Biden camp.

Spokesman Steven Cheung, who was also outside the court, said the Democrats’ campaign was in “complete freakout mode” over Trump’s resilience despite the multiple criminal cases against him.

“Joe Biden is losing nationally,” Jason Miller, another Trump spokesman, said.

“President Trump’s numbers continue to rise. And the best that Biden can do is roll out a washed-up actor.”

In his most biting comments, De Niro spoke of Trump through the lens of the largely Democratic city whose voters know Trump well and roundly rejected him at the polls.

“We New Yorkers used to tolerate him when he was just another grubby real estate hustler masquerading as a big shot, a two-bit playboy lying his way into the tabloids,” he said.

“A clown … No one took him seriously. They take him seriously now.”

The twin media conferences outside the New York courtroom came as Trump’s hush money trial nears its end.

Trump’s lawyer told jurors on Tuesday that prosecutors had failed to prove the former president was guilty of falsifying documents as the defence team began its closing argument.

Trump’s team was to be followed by prosecutors, who will sum up the witnesses and evidence they have presented as they argue Trump illegally falsified business documents to cover up a payment that ensured former adult star Stormy Daniels would not go public with her story of a 2006 sexual encounter.

Jurors are likely to begin deliberations as soon as Wednesday.

Elsewhere, a Reuters/Ipsos poll last week found Trump and Biden effectively tied for the presidency.

-with AAP