The impeachment trial of former US President Donald Trump intensified on Wednesday, with Democrats showing footage of him alleging election irregularities to supporters.

The second day of the trial began with opening statements delivered by Democratic House managers, who are presenting the case for impeachment.

Trump is alleged to have incited an insurrection at the Capitol, which was stormed by his supporters on January 6.

A Democrat Representative showed videos of Trump taken around the voting day of the presidential election in November. The footage showed Trump claiming to supporters that there were irregularities in the election, despite a lack of clear evidence.

The Representative alleged that Trump fanned his supporters' frustration which led to the violent attack on the Capitol. The lawmaker said Trump's responsibility for the incident was clear.

Trump's lawyers are scheduled to make their case following the opening statements, which are due to continue through Thursday. They are expected to plead his innocence on the grounds of freedom of expression.

At a US impeachment trial, a two-thirds majority in the Senate must vote to convict.

The ongoing trial is expected to find Trump not guilty, with many Republicans standing by their stance that the trial itself is unconstitutional.

There are also concerns among Democrats over the potential impact of a prolonged impeachment trial on Congressional debate on bills as well as the appointment of officials by the administration of President Joe Biden.

Many analysts say a verdict is likely to be reached soon.