The US House of Representatives on Wednesday impeached President Donald Trump for a second time, a first in American history, charging him with “incitement of insurrection” one week after he egged on a mob of supporters that stormed the Capitol while Congress met to formalise President-elect Joe Biden’s victory.

Democrats moved swiftly to impeach Mr Trump after the assault, which unfolded after he told supporters at a rally near the National Mall to march on the Capitol in an effort to get Republicans to overturn his defeat.

At least five people, including a Capitol Police officer, died during the siege and in the immediate aftermath.

The process is taking place with extraordinary speed and will test the bounds of the impeachment process, raising questions never contemplated before. Here’s what we know.

Impeachment is one of the Constitution’s gravest penalties.

Impeachment is one of the weightiest tools the Constitution gives Congress to hold government officials, including the president, accountable for misconduct and abuse of power.

• Related: American democracy is bruised and sore, so what happens next?

Members of the House consider whether to impeach the president – the equivalent of an indictment in a criminal case – and members of the Senate consider whether to remove him, holding a trial in which senators act as the jury.

The test, as set by the Constitution, is whether the president has committed “treason, bribery, or other high crimes and misdemeanours”.

The House vote requires only a simple majority of lawmakers to agree that the president has, in fact, committed high crimes and misdemeanours; the Senate vote requires a two-thirds majority.

The charge against Mr Trump is ‘incitement of insurrection.’

The article, drafted by Reps. David Cicilline of Rhode Island, Ted Lieu of California, Jamie Raskin of Maryland and Jerrold Nadler of New York, charges Mr Trump with “incitement of insurrection,” saying he is guilty of “inciting violence against the government of the United States”.

“If you don’t fight like hell, you’re not going to have a country any more,” Mr Trump told supporters before the Capitol riots on January 6. Photo: Getty

The article cites Mr Trump’s weeks-long campaign to falsely discredit the results of the November election, and it quotes directly from the speech he gave on the day of the siege in which he told his supporters to go to the Capitol.

“If you don’t fight like hell,” he said, “you’re not going to have a country any more.”

Proponents say impeachment is worthwhile even though Mr Trump has only days left in office.

While the House moved with remarkable speed to impeach Mr Trump, a Senate trial to determine whether to remove him cannot begin until January 19, his final full day in office. That means any conviction would almost certainly not be completed until after he leaves the White House.

Democrats have argued that Mr Trump’s offence – using his power as the nation’s leader and commander in chief to incite an insurrection against the legislative branch – is so grave that it must be addressed, even with just a few days remaining in his term.

To let it go unpunished, Democrats argued, would set a dangerous precedent of impunity for future presidents.

The biggest consequence for Mr Trump could be disqualifying him from holding office again.

Conviction in an impeachment trial would not automatically disqualify Mr Trump from future public office. But if the Senate were to convict him, the Constitution allows a subsequent vote to bar an official from holding “any office of honour, trust or profit under the United States”.

That vote would require only a simple majority of senators.

Such a step could be an appealing prospect not just to Democrats, but also to many Republicans who either have set their sights on the presidency themselves or are convinced that it is the only thing that will purge Mr Trump from their party. Senator Mitch McConnell of Kentucky, the Republican leader, is said to hold the latter view.

There is no precedent, however, for disqualifying a president from future office, and the issue could end up before the Supreme Court.

A Senate trial most likely won’t start until after Mr Biden becomes president.

Speaker of the House Nancy Pelosi holds a signed article of impeachment against President Donald Trump at the US Capitol on January 13. Photo: Getty

Democrats who control the House can choose when to send their article of impeachment to the Senate, at which point that chamber would have to immediately move to begin the trial.

But because the Senate is not scheduled to hold a regular session until January 19, even if the House immediately transmitted the charge to the other side of the Capitol, an agreement between Senate Republican and Democratic leaders would be needed to take it up before then.

Senator McConnell said on Wednesday that he would not agree to do so, meaning that the proceeding could not be taken up until the day before Mr Biden is sworn in.

Since time is needed for the Senate to set the rules for an impeachment trial, that means the proceeding probably would not start until after Mr Biden was president, and Democrats had operational control of the Senate.

“Given the rules, procedures and Senate precedents that govern presidential impeachment trials, there is simply no chance that a fair or serious trial could conclude before President-elect Biden is sworn in next week,” Senator McConnell said.

“In light of this reality, I believe it will best serve our nation if Congress and the executive branch spend the next seven days completely focused on facilitating a safe inauguration and an orderly transfer of power to the incoming Biden administration.”

-New York Times