WASHINGTON — US Attorney General Jeff Sessions was fired by Donald Trump Wednesday after enduring more than a year of bitter criticism from the president over his decision to step aside from the Russia investigation that has dogged the White House.

The move cast into doubt the ability of Special Counsel Robert Mueller -- who had until now been insulated from White House interference -- to complete the Russia probe, and drew stern warnings from Democrats for the president to stay clear.

Sessions’ departure came the day after a midterm vote that saw Republicans lose control of the House of Representatives but boost their Senate majority, and Trump’s swift move was seen as a sign of how he confident he was feeling after the polls.

In announcing the resignation -- in a tweet thanking him "for his service" -- Trump right away named as acting attorney general Sessions’ chief of staff Matthew Whitaker.

That set off immediate alarm bells: Whitaker has been overtly critical of the broad scope granted to Mueller’s team to probe beyond allegations Trump’s campaign colluded with Russia in 2016, into other ties between Trump, his family and aides, and Russia -- an investigation the president calls a "witch hunt".

In an op-ed in August last year he publicly urged Deputy Attorney General Rod Rosenstein -- who oversees the probe -- to "limit the scope of his investigation to the four corners of the order appointing him special counsel."

As acting attorney general, Whitaker now has the power to wrest oversight away from Rosenstein, and take charge himself.

First casualty after midterms

Senator Mark Warner, senior Democrat on the Senate Intelligence Committee, was among those who sounded a warning to Trump.

"No one is above the law and any effort to interfere with the special counsel’s investigation would be a gross abuse of power by the president," he said.

Democratic Congressman Jerry Nadler, who is expected to take charge of the House Judiciary Committee in the wake of Tuesday’s elections, was more direct:

"There is no mistaking what this means, and what is at stake: this is a constitutionally perilous moment for our country and for the president."

Sessions was the first casualty of a cabinet shakeup that had been expected from Trump following the midterm elections.

But his departure had been anticipated since early this year, after he endured withering and repeated criticism from the president over the legally troubled ban on Muslim travelers Trump sought when he came into office, and over the Mueller probe.

"At your request, I am submitting my resignation," Sessions said in the first line of a letter addressed to Trump, released by the Department of Justice.

Trump’s first backer

Sessions was the first US senator to back Trump’s presidential run in 2016, giving the New York real estate billionaire credibility against a broad field of Republican stalwarts.

The two were reportedly brought together by a shared wish to crack down on immigration.

After taking office in January 2017, the former Alabama prosecutor launched tough law-and order policies and a broad ban on Muslim travelers promised by Trump during the campaign.

He was in the vanguard of administration pushes to expand the ranks of federal law enforcement, fill courts with conservative judges, and crack down on Central American gangs like MS-13.

But the president was infuriated when in March 2017 Sessions recused himself from the nascent Russia investigation, because of his own Russian contacts during the 2016 campaign. Instead, he gave Rosenstein that authority.

When Trump weeks later fired FBI director James Comey in anger at the Russia investigation, Rosenstein stunned the administration by naming Mueller, a former FBI chief, to lead the probe as an independent prosecutor.

That structure, with Sessions recused and Rosenstein supervising Mueller, has insulated the investigation from outside interference.Still, Trump has repeatedly accused Mueller of running an illegal investigation staffed by Democrats and threatened to shut it down.

Indictments looming

Matters though were clearly coming to a head after Mueller racked up indictments against 34 people and three companies, in direct and spinoff cases.

Eight guilty pleas have resulted, and one jury trial conviction.

Most notably, several top Trump aides have agreed to cooperate: former national security advisor Michael Flynn; former campaign chair Paul Manafort; former vice chair Richard Gates; and former Trump Organization vice president Michael Cohen, long Trump’s personal fixer.

Mueller was expected to unveil in the coming weeks new indictments, possibly against 2016 campaign consultant Roger Stone and Trump’s son Donald Jr.

Moreover, Mueller’s team and the White House have been haggling for months over whether the president himself would answer questions. Mueller is known to be examining whether Trump obstructed justice in firing Comey and other acts.

In addition, the White House has shown concern that Mueller is investigating the finances of the Trump Organization and links to Russia.

That is where Whitaker could serve the president’s interests. In his op-ed last year he declared in particular that Trump family finances fall "completely outside the realm of his 2016 campaign (and) beyond the scope of the appointment of the special counsel." — AFP