Former FBI Director James Comey explained what could happen if President Donald Trump fired the special counsel Robert Mueller.

Trump has been enraged by Mueller's investigation into Russia's meddling in the 2016 US election and whether the Trump campaign colluded with Moscow to influence the outcome — prompting the president to consider dismissing Mueller.

But Comey said a dismissal would be "ineffective" and perceived by his subordinates and ordinary Americas as "disastrous."

Former FBI Director James Comey explained what could happen if President Donald Trump fired the special counsel Robert Mueller — and said it would most likely bring about a crisis.

Mueller has often ruffled the president's feathers with his investigation into whether the Trump campaign colluded with Russia to influence the outcome of the 2016 US election and whether Trump subsequently attempted to obstruct justice.

The president has on numerous occasions expressed his dissatisfaction with the investigation and desire to have it end. As Trump is ultimately in charge of the Justice Department, of which Mueller is an employee, he could technically dismiss Mueller — but that would come with huge risks.

Speaking at an event on Monday to promote his new book, "A Higher Loyalty," Comey said that firing Mueller "would be utterly ineffective in practice" because "you'd have to fire the entire FBI and the entire Justice Department," according to the news website Axios.

"I don't know that if the president followed the normal course, he would be able to find an executive who would carry out an order to fire Robert Mueller," Comey added, according to Axios. "And so then maybe he does away with the regulation that appointed Mueller and then fires him."

The White House has suggested that Trump believes he has the power to dismiss Mueller. But critics have said that such a move could lead to a "constitutional crisis."

"I would hope it would be disastrous in the eyes of the American people without regard to their political affiliation, but it would also be ineffective," Comey said, per Axios. "So don't do disastrous things at all. Don't do disastrous things that won't make a difference."

Comey has emerged as a critic of Trump since the president fired him last May. Trump has responded to Comey's recent book tour and related publicity by lodging a litany of complaints about Comey's performance at the FBI and suggesting he be jailed.