President Donald Trump, already facing mounting calls to step down or risk impeachment, suffered further ignominy on Friday when Twitter permanently suspended his account, saying the US leader is too dangerous to use the platform.

After a "close review" of tweets from the @realDonaldTrump account, "we have permanently suspended the account due to the risk of further incitement of violence," Twitter said.

The unprecedented move, which severs Trump from his 88.7 million followers, is an astounding setback for the president in the chaotic waning days of his administration.

It could also prove an insurmountable hurdle should the brash Republican choose to mount a political comeback in 2024, as he has hinted he could do on multiple occasions.

With his presidency imploding, Trump signalled a final, unrepentant display of division by announcing — in his final tweet before the ban — that he will skip the inauguration of Joe Biden on January 20.

"To all of those who have asked, I will not be going,” he tweeted.

Biden responded this was "a good thing”, branding Trump an "embarrassment”.

However, Biden showed how wary he is of the growing rush to impeach Trump — and deepen the nation’s political divisions — over his incitement of crowds who stormed Congress on Wednesday.

"That is a judgement for the Congress to make,” Biden said, adding that the "quickest” way to get Trump out was for him and Vice President-elect Kamala Harris to take over in 12 days.

"I am focused now on us taking control as president and vice president on the 20th and to get our agenda moving as quickly as we can.”

Two days after Trump sent a mob of followers to march on Congress, his presidency is in freefall, with allies walking away and opponents sharpening their teeth.

House Speaker Nancy Pelosi warned that Democrats will launch impeachment proceedings unless Trump resigns or Vice President Mike Pence invokes the 25th Amendment, where the Cabinet removes the president.

"If the President does not leave office imminently and willingly, the Congress will proceed with our action,” Pelosi wrote.

In a jaw-dropping moment, Pelosi revealed she had spoken on Friday with the Chairman of the Joint Chiefs of Staff Mark Milley about "preventing an unstable president from initiating military hostilities or accessing the launch codes and ordering a nuclear strike”.

"The situation of this unhinged President could not be more dangerous, and we must do everything that we can to protect the American people,” Pelosi wrote.

House Democrats, who already impeached Trump in a traumatic, partisan vote in 2019, said the unprecedented second impeachment of a president could be ready next week.

"We can act very quickly when we want to,” Representative Katherine Clark told CNN.

A draft impeachment resolution being circulated would charge Trump with a single article: "incitement of insurrection”.

Whether Republican leaders of the Senate would then agree to hold a lightning-fast impeachment trial before the transition is another matter.

But Republican Senator Ben Sasse told CBS News he would "definitely consider” articles of impeachment if and when they are introduced, while Senator Lisa Murkowski became the chamber’s first Republican to openly call for Trump’s resignation.

In the House, top Republican Kevin McCarthy said: "Impeaching the president with just 12 days left in his term will only divide our country more.”

Too little, too late

Trump, whose actions Wednesday capped his relentless efforts to overturn Biden’s November 3 election win, finally conceded defeat on Thursday and appealed for calm.

"A new administration will be inaugurated on January 20. My focus now turns to ensuring a smooth, orderly and seamless transition of power,” Trump said in a short video.

However, the evidently reluctant concession, in which Trump failed to congratulate Biden or directly admit defeat, was too little, too late to calm outrage over his role in the Capitol invasion.

Five people died in the mayhem, including one woman who was shot dead and a US Capitol Police officer. Flags over the Capitol were lowered to half-staff on Friday.

Government exit

Education Secretary Betsy DeVos became the second Cabinet member to quit, after Transportation Secretary Elaine Chao, telling Trump in a letter that such "behaviour was unconscionable for our country”.

Multiple lower-level officials have also left. According to reports, the only reason the trickle has not turned into a flood is the decision by senior figures to try to maintain stability during the transition to Biden.

Trump, however, appears to have lost the grip he once exercised on both the Republican Party and his own staff as he rampaged through his turbulent four-year presidency.

Speaking to CNN, retired Marine Corps general John Kelly, who served as Trump’s chief of staff for 18 months, said the Cabinet should consider the 25th Amendment but believed the president had already been put into a box.

"He can give all the orders he wants but no one is going to break the law,” Kelly said.

Trump banned, but not ‘Ayatollah’

After the ban, Trump took to the official @POTUS account to accuse Twitter of "trying to silence me”.

"Twitter has gone further and further in banning free speech, and tonight, Twitter employees have coordinated with the Democrats and the Radical Left in removing my account from their platform, to silence me — and YOU, the 75,000,000 great patriots who voted for me,” he said.

The post was swiftly deleted by Twitter.

Twitter also suspended Trump’s campaign account @TeamTrump.

With the president muted, son Donald Trump Jr took to Twitter to call the platform’s move "absolute insanity”.

While his father is banned, "the ayatollah, and numerous other dictatorial regimes can have Twitter accounts with no issue despite threatening genocide to entire countries and killing homosexuals etc”, Trump Jr steamed.

Founder of communist China Chairman "Mao would be proud,” he said.

In a blog post, Twitter explained that the suspension was based on factors such as evidence that plans for future armed protests were proliferating on and off the platform, "including a proposed secondary attack on the US Capitol and state capitol buildings on January 17, 2021”.

Biden, who won seven million votes more than Trump, as well as a decisive majority in the vital state-by-state Electoral College, will be sworn in on the Capitol Steps under huge security.

Between drastic COVID-19 crowd restrictions, the absence of Trump, and a new "unscalable” fence around the congressional complex, very little about the inauguration will be business as usual