Now a private citizen, Trump is stripped of his protection from legal liability that the presidency gave him.

That change in status is something that even Republicans who voted on Saturday to acquit of inciting the January 6 attack are stressing as they urge Americans to move on from impeachment.

"President Trump is still liable for everything he did while he was in office, as an ordinary citizen, unless the statute of limitations has run," Senate Minority Leader Mitch McConnell of Kentucky said after that vote.

He insisted that the court were a more appropriate venue to hold Trump accountable than a Senate trial.

"He didn't get away with anything yet," McConnell said. "Yet."

The insurrection at the Capitol, in which five people died, is just one of the legal cases shadowing Trump in the months after he was voted out of office.

He also faces legal exposure in Georgia over an alleged pressure campaign on state election officials, and in Manhattan over hush-money payments and business deals.

But Trump's culpability under the law for inciting the riot is by no means clear-cut. The standard is high under court decisions reaching back 50 years.

Trump could also be sued by victims, although he has some constitutional protections, including if he acted while carrying out the duties of president. Those cases would come down to his intent.

Legal scholars say a proper criminal investigation takes time, and there are at least five years on the statute of limitations to bring a federal case. New evidence is emerging every day.

"They're way too early in their investigation to know," said Laurie Levenson, a law professor at Loyola Law School and former federal prosecutor.

"The have arrested 200 people, they're pursuing hundreds more, all of those people could be potential witnesses because some have said 'Trump made me do it'."

What's not known, she said, is what Trump was doing during the time of the riot, and that could be the key.

Impeachment didn't produce many answers. But federal investigators in a criminal inquiry have much more power to compel evidence through grand jury subpoenas.

"It's not an easy case, but that's only because what we know now, and that can change," Levenson said.

The legal issue is whether Trump or any of the speakers at the rally near the White House that preceded the assault on the Capitol incited violence and whether they knew their words would have that effect.

That's the standard the Supreme Court laid out in its 1969 decision which overturned the conviction of a Ku Klux Klan leader.

Trump urged the crowd on January 6 to march on the Capitol, where Congress was meeting to affirm Joe Biden's presidential election.

Trump even promised to go with his supporters, although he didn't in the end.

"You'll never take our country back with weakness," Trump said.

Trump's impeachment lawyers said he didn't do anything illegal. Trump, in a statement after the acquittal, did not admit to any wrongdoing.

Federal prosecutors have said they are looking at all angles of the assault on the Capitol and whether the violence had been incited.

The attorney general for the District of Columbia, Karl Racine, has said that district prosecutors are considering whether to charge Trump under local law that criminalises statements that motivate people to violence.

"Let it be known that the office of attorney general has a potential charge that it may utilise," Racine told MSNBC last month.

The charge would be a misdemeanour with a maximum sentence of six months in jail.

Trump's top White House lawyer repeatedly warned Trump on January 6 that he could be held liable. That message was delivered in part to prompt Trump to condemn the violence that was carried out in his name and acknowledge that he would leave office January 20, when Biden was inaugurated. He did depart the White House that day.

Since then, many of those charged in the riots say they were acting directly on Trump's orders. Some offered to testify.

A phone call between Trump and House Republican leader Kevin McCarthy emerged during the impeachment trial in which McCarthy, as rioters stormed the Capitol, begged Trump to call off the mob.

Trump replied: "Well, Kevin, I guess these people are more upset about the election than you are."

The McCarthy call is significant because it could point to Trump's intent, state of mind and knowledge of the rioters' actions.

Court cases that try to prove incitement often bump up against the First Amendment. In recent years, federal judges have taken a hard line against the anti-riot law.

It's possible federal prosecutors will decide not to bring charges, and if Trump were indicted in one of the many other separate investigations, federal prosecutors could decide justice would be done elsewhere.

Atlanta prosecutors have recently opened a criminal investigation into Trump's attempts to overturn his election loss in Georgia, including a January 2 phone call in which he urged that state's secretary of state, Brad Raffensperger, to "find" enough votes to reverse Biden's narrow victory.

Australian Associated Press