In the wake of former FBI director James Comey's damning allegations against Donald Trump at the Senate intelligence committee hearing, some Democrats have been calling on the U.S. president to make his own appearance at such a forum.

"The American people deserve to hear the president's side of the story in a similar forum — under oath and open to the press," Senator Chris Murphy of Connecticut said in a statement.

But could Trump be compelled to testify at a congressional hearing if a request was made?

"Nothing compels him to go," said Jonathan Turley, a George Washington University law professor and noted constitutional scholar. "Presidents are not historically called before Congress."

Mark Rozell, dean of George Mason University's Schar School of Policy and Government, agreed.

"A president could easily claim executive privilege to avoid himself going before Congress, and there is no constitutional basis to claim that the legislative branch has superiority over the executive to make the president subservient to its demands."

Could Trump be compelled to testify at a congressional hearing, such as the one where former FBI director James Comey testified? Unlikely. (J.Scott Applewhite/Associated Press)

It's safe to say that it's not just Democrats, but the general public who would be eager to see the president appear before a committee and lay out his version of his meetings with Comey.

Comey made a number of troubling statements about Trump at a Senate intelligence committee hearing on Thursday. He accused the president of lying and of demanding a loyalty pledge. He said Trump pressured him to drop a Russia-related probe into former national security adviser Michael Flynn and fired him when that didn't happen.

On Friday during a news conference, Trump denied those allegations, effectively accusing Comey of lying under oath to Congress.

A rare step for a president

But it's still a big leap to think that Trump would be willing to take the rare step for a president and testify before a congressional committee in a public forum. Currently, the House and Senate intelligence committees have launched their own Russia-related investigations.

A few presidents have voluntarily appeared before congressional committees, most recently Gerald Ford, who was questioned before the House judiciary committee to explain his pardon of former president Richard Nixon.

"But that's a rare exception," said Turley. "While the president's underlings can be called before Congress, committees have not historically called presidents themselves."

Michael Gerhardt, a law professor at the University of North Carolina, said constitutional scholars don't necessarily agree on whether Trump could be compelled to testify at one of these committees.

"Some people argue that compelling the president undermines his authority, oversteps congressional bounds, weakens him, enlarges the power of Congress," he said. "For all those different reasons, it would be inappropriate."

But others argue that on balance it's not that costly to the president, and there's an upside in trying to verify the information, Gerhardt said.

"But I think the president would not be on weak ground to say, 'Look, this is literally trying to take control of the presidency, take control of my time and physical presence, and that's just something Congress can't do.'"

Trump agreed he would speak with special counsel Robert Mueller, above, who is investigating whether Russia meddled in the 2016 presidential election and whether members of the Trump campaign team co-ordinated efforts with officials from Moscow. (Andrew Burton/Getty)

It's possible that Congress could issue a legislative subpoena for Trump to testify and, if he refused to appear, litigate it all the way to the Supreme Court, Gerhardt said.

Currently, Republicans are in control of the House and Senate and chairing all the committees, meaning the odds that they would try to order Trump to appear before a committee hearing are extremely low. But if the 2018 midterms shake things up, that could change the dynamic.

Trump's '100%' promise

But at Friday's news conference, Trump told reporters that "100 per cent" he would testify under oath to give his version of conversations he had with Comey.

He seemed to be promising, however, that he would speak with special counsel Robert Mueller, not in a public forum.

Mueller is investigating whether Russia meddled in the 2016 presidential election and whether members of the Trump campaign team co-ordinated efforts with officials from Moscow.

If Trump was to renege on his "100 per cent" pledge to testify under oath with Mueller, the special counsel could subpoena him.

The Supreme Court, in the Paula Jones sexual harassment civil suit case against Bill Clinton, determined that the president could be compelled to appear for a deposition. But Trump, who has the same protections as all citizens, could invoke his right against self-incrimination. A refusal to co-operate with the special counsel, however, would just magnify the problems for the White House, Turley said.

"When a president declines to co-operate with a special counsel appointed by his own Justice Department, we move into a much more problematic stage," he said.

Rozell said that Trump deciding to testify under oath may be his best move and would show that he is not afraid of the truth.

"Making a strong case for himself while under questioning is risky, but it may be his best chance to convince the public that he is being honest."

Gerhardt said there is not much downside for him to testify under oath.

"He can discount or downplay what he said or, as he has suggested, directly contradict Comey. If the latter, then we are back to the he-said he-said situation we started with."