Donald Trump took his seat Monday in the New York courtroom, becoming the first ex-president in US history to stand criminal trial, a seismic moment in the already explosive 2024 presidential campaign.

The Republican struck a defiant stance, telling a throng of journalists outside the gritty Manhattan courthouse that his trial was an "outrage" and an "assault on America."

He then strode into the courtroom, walking past nine rows of wooden benches with a stern expression and followed by his legal team.

The scandal-plagued 77-year-old is accused of falsifying business records in a scheme to cover up an alleged sexual encounter with adult film actress Stormy Daniels to shield his 2016 election campaign from a last-minute upheaval.

The so-called hush money affair is only one of four criminal cases hanging over Trump, including historic prosecutions against the Republican's alleged attempts to subvert the 2020 election and prevent the winner, Joe Biden, from taking office.

If convicted in the hush money case, Trump would potentially face years in prison, but legal observers consider this unlikely.

Even so, the prospect of Trump becoming a convicted felon throws an unprecedented wild card into an already unpredictable November 5 election, where he wants to defeat Biden and return to power.

The hard-right populist is running on dark vows of "vengeance" and seeking to spin his criminal cases as evidence of persecution.

On Monday his campaign released a video portraying Trump with the trappings of the presidency and warning his supporters that "they want to take away my freedom because I will never let them take away your freedoms."

Attempting to keep up his trademark bravado, Trump said last week that he will take the stand in the trial -- a highly unusual and often risky move for defendants.

 Lawyer and porn star 

 The trial starts with what could be multiple days of jury selection. A pool of ordinary citizens convened by Judge Juan Merchan must answer a questionnaire including checks on whether they have been members of far-right groups.

The actual charges revolve around highly technical finance laws.

Trump is accused of illegally covering up remittances to his longtime attorney and fixer Michael Cohen, who was using the funds to pay Stormy Daniels to keep quiet about the alleged sexual encounter in the final weeks of the 2016 election campaign.

A New York grand jury indicted Trump in March 2023 over the payments made to Daniels, whose real name is Stephanie Clifford, with the ex-president charged with 34 counts of falsifying business records.

He denies the charges and says the encounter with Clifford and another with a Playboy nude model, whose story he also allegedly covered up, did not happen.

Trump also claims he will not get a fair trial in heavily Democratic New York.

Even if convicted, he would be able to appeal and would not be barred from continuing to run, or even being elected president on November 5.

 Four criminal cases 

 Trump's other three criminal cases -- centered on his alleged hoarding of top-secret documents in Florida after he left the White House and his involvement in attempts to overturn the 2020 election -- all face multiple delays.

In the New York case, Trump has repeatedly failed to secure meaningful delays, and Merchan has signaled he will run the trial with a firm hand.

Last week, the judge extended an existing gag order, in place to prevent Trump from attacking those involved in the trial, widening it to cover family members of the judge and Manhattan District Attorney Alvin Bragg, the lead prosecutor.

The expansion of the order came after Trump lashed out at Merchan and his daughter in a series of posts on Truth Social.