Donald Trump's sacking of FBI director James Comey is an "abuse of power" that will "result in a crisis with Congress", according to the chief White House ethics lawyer during the George W Bush administration.
"Director Comey certainly made some very serious mistakes over the past several months," Richard Painter told 7.30.
"But the fact of the matter is that he is now in the middle of the investigation of the collusion between Russia and some of the Trump campaign people with respect to the Russian espionage going on in the United States last year.
"That's a critically important investigation."
Mr Painter said it was crucial Mr Trump appointed an independent prosecutor to continue the investigation.
"If we don't have an independent prosecutor, no-one is going to trust the result of an investigation undertaken by an FBI supervised by President Trump and his Justice Department," he said.
"We are in a very, very serious situation right now."
He predicts that without an independent prosecutor, Mr Trump runs the risk of a crisis with Congress.
"The Russian investigation is critical to our national security," he said.
"We need to go full steam ahead and get the facts, and to sack the FBI director in the middle of that is going to undermine the investigation.
"And there is no plan, on the part of Donald Trump, to put someone in there who is going to be independent.
"So, I think this could be a very difficult situation with Congress and ultimately the American people."
Comparison with Richard Nixon and Watergate
Many critics of Donald Trump's sacking of James Comey are making comparisons with disgraced former president Richard Nixon, when he sacked special prosecutor Archibald Cox in 1973.
"Archibald Cox was getting a little bit too close to the collusion and the cover-up going on inside the Nixon White House of the Watergate break-in," Mr Painter said.
"President Nixon wanted to fire the special prosecutor, he asked the attorney-general to do so and the attorney-general resigned. He refused to do so.
"And then the next acting attorney-general also refused and he had to get to his third attorney-general — in the course of one day — in order to get the special prosecutor fired.
"The other two attorneys-general had said, 'No, of course we can't fire a special prosecutor in the middle of an investigation that concerns the president. It's an abuse of power by the president'.
"Ultimately that led to President Nixon being forced from office.
"So, President Trump is not doing the right thing here."
Suing Donald Trump
Mr Painter already had serious concerns about Mr Trump's presidency before this latest controversy.
He is , as all presidents have done for the past 40 years.
Mr Painter argues that by refusing to do this, Mr Trump is violating the US constitution.
Mr Trump's son, Eric, has dismissed the action as "harassment for political gain".
However, Mr Painter thinks the concerns over the Trump presidency are not confined to just one side of politics.
"I think we're reaching a point where members of both political parties are getting fed up with the abuse of power by the Trump administration," he said.
"It's just scandal after scandal and people are getting quite fed up."