His loyalty went unrewarded - Mr Trump reportedly left it to his Chief of Staff, John Kelly, to tell Mr Sessions the President wanted him to step down. But President Trump's decision to request Sessions' resignation raises serious concerns about his commitment to the rule of law in the United States.
Senator Chris Murphy, a Democrat representing CT, took issue with the language around Sessions' resignation, noting the embattled AG was sacked by his boss and did not leave voluntarily.
A permanent replacement for Sessions must be confirmed by the US Senate, which Mr Trump's Republicans will continue to control as a result of the midterm elections.
During a press conference at the White House Wednesday, President Trump said he is satisfied with the performance of "most of his Cabinet", but left room for major changes in the coming days and weeks.
Asked if he sees this move as an attempt to undermine the investigation, Dean said yes.
In the past Mr Whitaker has called for limits to be put on the Mueller investigation saying any investigation into Mr Trump's finances is going too far.
"He will serve our Country well", said Trump of Whitaker.
But there has also been speculation Mr Trump could try to kill or suppress the 18 month-old probe, pressing his view that Mr Mueller leads a team staffed by Democrats operating under an illegal mandate. They could also explore the possibility of impeachment.
"It is impossible to read Attorney General Sessions' firing as anything other than another blatant attempt by @realDonaldTrump to undermine & end Special Counsel Mueller's investigation", House Minority Leader Nancy Pelosi tweeted following Sessions' resignation.
Now Whitaker, 49, leads everything at the Justice Department - including the Russian Federation probe.
To Mr Trump's great anger, on March 2, 2017, Mr Sessions recused himself from involvement in and oversight of the nascent Russia collusion investigation because of his own Russian contacts during the 2016 campaign.