Jeff Sessions, the Alabama Republican was the first US senator to endorse Trump and was a close campaign aide who introduced Trump in a red "Make America Great Again" hat. He supported Trump's crime-fighting agenda and particularly his immigration enforcement policies.
But the Mueller investigation resulted in an irreparable rift in their relationship. During his confirmation hearing, Sessions said that he had never met with the Russians during the campaign. But when the Justice Department, in response to a Washington Report acknowledged that Sessions had actually 2 encounters with the then Russian ambassador during the campaign, Sessions recused himself.
This caused a furore in the White House. Sessions rejected the entreaty not to step aside.
Trump accused Sessions on Twitter of not protecting Republican interests and belittled Sessions with blistering remarks over his recusal from the Russia investigation.
Sessions was once considered to be too eager to do Trump's bidding as in the case of firing the former FBI deputy director Andrew McCabe just before he was to have retired. But though he continued to praise Trump's political agendas during his tenure, he could never find favour with Trump again.
Mueller who took over the investigation began examining if Trump's attitude towards Sessions was an effort to obstruct the probe.
Sessions gradually lost the support of the Senate Republicans when Judiciary Committee Chairman Chuck Grassley suggested he might schedule a confirmation hearing for another attorney general if Trump fired him.
Sessions told the President that he was submitting his resignation "at your request".
Trump tweeted that he was naming Sessions' chief of staff Mathew Whitaker, a former US attorney from Iowa, as acting attorney general.