Washington - President Donald Trump intensified his assault on Attorney General Jeff Sessions on Wednesday, in an apparent bid to force his one-time ally from office and regain influence over a Russia investigation eating away at the administration.For the fourth time in a week, Trump laid into one of his earliest endorsers, now demanding to know why Sessions has not fired the acting FBI director.Trump appears to be trying to force the former Alabama senator from office, allowing the president to replace Sessions with someone who has not recused himself from the investigation into possible collusion between Russia and the Trump campaign in last year's election.In norm-smashing tweets that further eroded the firewall between politics and the Justice Department, Trump accused acting FBI director Andrew McCabe of being a "friend" of James Comey - the FBI chief whom Trump fired over the Russia investigation - and questioned his wife's ties to Hillary Clinton. "Why didn't A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got big dollars ($700 000) for his wife's political run from Hillary Clinton and her representatives. Drain the Swamp!"Trump's new barb at Sessions came as the embattled attorney general visited the White House for what his spokespersonn described as a "routine" meeting of cabinet principals.White House sources said Sessions and Trump had no plans to meet.High risks Trump's brutal show of strength carries high risks for the president.In private, cabinet members are reportedly expressing unease at the treatment of their colleague.And as a former senator, Sessions retains some support among lawmakers who would ultimately have to approve his replacement.The saga has also prompted questions about Trump's attitude toward the rule of law and rekindled allegations he is trying to quash the investigation or obstruct justice. A new attorney general, unencumbered by Sessions' Russia recusal, would have the power to fire the special prosecutor investigating the issue. Trump's behaviour has also raised questions about why he does not simply fire Sessions. If Sessions stares down the humiliation - as allies say he will - it would make the president look weak.White House Press Secretary Sarah Huckabee Sanders indicated on Tuesday that Trump was not going to change his mind about Sessions.Communications director Anthony Scaramucci said the situation would "get to a resolution soon".