New York, New York - Donald Trump could not have made his stance clearer: he would rather be anywhere else than in a New York courtroom Tuesday, on trial for business fraud.

Dressed in a blue suit with a blue tie, the 77-year-old former US president shifted between discomfort and anger as he sat through the second day of the historic proceeding, the first criminal trial of a US president.

"This is a trial that should have never been brought," Trump told reporters outside the courtroom as he lashed out against President Joe Biden, his Democratic rival in the November presidential election, and the "Trump-hating judge" in the case.

"Every legal pundit and every legal scholar said this trial is a disgrace," he added.

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Trump is accused of falsifying business records in a scheme to cover up reports on the eve of his 2016 election victory that he had an extramarital affair with adult film star Stormy Daniels.

After a brief exchange with his lawyers Tuesday, Trump took a seat at the defense table and only seemed to lighten up when photographers were brought in to take photos of him before the trial.

The day was devoted to jury selection, with prosecutors and lawyers quizzing potential jurors in a bid to find 12 New Yorkers deemed impartial enough to decide the fate of the scandal-hit billionaire.

Trump, who is under a partial gag order restricting him from attacking individuals connected to the case, sat in silence and kept his gaze on the jury box.

Despite his quietude in the courtroom, the former president did not mince words on social media.

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"MY TRIAL IS AN ASSAULT ON AMERICA!" he wrote on Truth Social early Tuesday.

Trump is facing three other criminal cases, stemming from 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.