The US Senate on Tuesday opened the historic second impeachment trial of Donald Trump, who stands accused of inciting insurrection on January 6, when the former president's supporters stormed Congress.

Trump is the first president ever to face two impeachment trials -- he was acquitted in 2020 of abuse of power -- as well as the first in history to be tried after leaving office.

"It's our solemn constitutional duty to conduct a fair and honest impeachment trial of the charges against former president Trump -- the gravest charges ever brought against a president of the United States in American history," Democratic Majority Leader Chuck Schumer said.

Democratic Senator Patrick Leahy is presiding over the trial, which will begin with hours of debate, followed by a vote, on the constitutionality of trying an ex-president.

This will almost certainly be just a formality as the Democrats have enough votes, but it will give early indication of how open Republicans are to the case at all.

The main part of the trial will start Wednesday, with each side having 16 hours to present oral arguments.

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