LIVE: Trump's second impeachment trial set to kick off today as Republicans continue defending him over the Capitol siege

• Trump's Senate impeachment trial starts Tuesday afternoon.
• He was impeached on a charge of incitement of insurrection over the January 6 Capitol siege.
• Scroll down to watch the trial and follow Insider's live coverage.

Former President Donald Trump's impeachment trial will kick off on Tuesday as the Senate weighs whether to convict him on a charge of incitement of insurrection. The first order of business: a debate over the constitutionality of holding an impeachment trial in the first place.

Watch the trial below:

The House of Representatives impeached Trump last month over his actions related to the deadly Capitol siege on January 6, as Congress was preparing to formalize President Joe Biden's victory in the 2020 US election.

The article of impeachment accused Trump of having "willfully made statements that, in context, encouraged - and foreseeably resulted in - lawless action at the Capitol." It went on to say that Trump "gravely endangered the security of the United States and its institutions of Government" and "threatened the integrity of the democratic system, interfered with the peaceful transition of power, and imperiled a coequal branch of Government."

"He thereby betrayed his trust as President, to the manifest injury of the people of the United States," the article of impeachment said, adding that Trump "has demonstrated that he will remain a threat to national security, democracy, and the Constitution if allowed to remain in office, and has acted in a manner grossly incompatible with self-governance and the rule of law."

The nine House impeachment managers who will act as prosecutors in the Senate trial filed a brief saying, "There is no 'January Exception' to impeachment or any other provision of the Constitution." It continued: "A president must answer comprehensively for his conduct in office from his first day in office through his last."

Trump's legal team pushed back in its own brief, saying it is unconstitutional to even hold the trial given that he is no longer in office and therefore can't be removed via a conviction in the Senate. His defense attorneys also argued that there's "insufficient evidence" to determine whether Trump's claims of election and voter fraud were accurate or not, and they rejected a Democratic request for him to testify in the proceedings.

Scroll down to follow Insider's live coverage of the historic event.

Trump's acquittal is virtually guaranteed

Trump addresses supporters in Washington DC on January 6, 2021, ahead of an attack on the US Capitol      Getty Images

The former president sparked widespread outrage in the immediate aftermath of the deadly Capitol insurrection. He was criticized for spending months spreading nonsense claims of election malfeasance and headlining a rally before the insurrection in which he called on his supporters to march to the Capitol and "fight like hell."

In the weeks since the riot, however, the majority of Republican lawmakers have rallied to Trump's defense, arguing that his Senate impeachment trial runs afoul of the Constitution.

Last month, 45 Senate Republicans voted to declare the trial unconstitutional, making it virtually impossible that enough of them will break ranks to reach the two-thirds majority required in the upper chamber to convict Trump and potentially bar him from ever holding public office again.

Trump's second impeachment was the most bipartisan in US history

Rep. Liz Cheney was one of ten Republicans who sided with Democrats in the vote to impeach Trump over the Capitol riot.      (Photo by Samuel Corum/Getty Images)

Trump is the only US president to have been impeached twice while in office.

In his first impeachment, one House Republican — then-Rep. Justin Amash — sided with Democrats to charge Trump with abuse of power and obstruction of Congress related to the Ukraine scandal. The then-Republican controlled Senate voted largely along party lines to acquit Trump, with Sen. Mitt Romney being the only Republican to join Democrats in voting to convict.

In Trump's second impeachment, 10 Republicans broke ranks to vote with their Democratic colleagues after the former president was accused of whipping his supporters into a frenzy and setting them loose on Congress. The final vote was the most bipartisan impeachment vote in US history.

The House Republicans who voted to impeach Trump were:

• Rep. Liz Cheney of Wyoming's At-Large Congressional District
• Rep. Jaime Herrera-Beutler of Washington's 3rd District
• Rep. Anthony Gonzalez of Ohio's 16th District
• Rep. John Katko of New York's 24th District
• Rep. Adam Kinzinger of Illinois's 16th District
• Rep. Peter Meijer of Michigan's 3rd District
• Rep. Dan Newhouse of Washington's 4th District
• Rep. Tom Rice of South Carolina's 7th District
• Rep. Fred Upton of Michigan's 6th District
• Rep. David Valadao of California's 21st District