Former Attorney General Jeff Sessions is considering running for the Alabama Senate seat he left in order to join Donald Trump's administration.

There are already five Republicans interested in the contest, including Roy Moore, who lost the seat to Democrat Doug Jones in 2017 special election amid allegation of sexual misconduct with teenage girls.

Sessions, 72, has until November 8 to decide - that is the filing deadline in the state, reports Politico.

Jones is seen as the most vulnerable Senate Democrat running for re-election next year and Sessions would be a formidable opponent if he ran.

Jeff Sessions is considering running for his old Alabama Senate seat

It's unclear how President Trump would react - he and Sessions had a falling out when Sessions wouldn't recuse himself from overseeing the Russia investigation

Sessions served in the Senate for two decades before he left to head the Justice Department for the president.

He was an early supporter of Trump's in the 2016 presidential campaign.

But their relationship quickly soured after Sessions recused himself from overseeing Special Counsel Robert Mueller's probe into allegations the Trump campaign colluded with Russia and the president obstructed the investigation.

Trump railed against his attorney general on Twitter and in interviews about the decision. The Mueller report found the president pressured Sessions into reversing his recusal, which he did not do.

Sessions resigned after the day after the 2018 midterm election at the president's request.

Trump told NBC in June that his selection of Sessions as his attorney general was his 'biggest mistake.'

'I would say if I had one do-over, it would be, I would not have appointed Jeff Sessions to be attorney general,' Trump told NBC's 'Meet the Press.'

The president won Alabama with 62 per cent in 2016.

Mueller found no evidence of collaboration on behalf of the Trump campaign and the Justice Department - now headed by Attorney General Bob Barr - opted not to pursue an obstruction of justice charge given long-standing policy not to indict a sitting president.

Roy Moore (left) is one of the five Republicans running for the right to take on Democratic Senator Doug Jones (right)

Rep. Bradley Byrne (top left), former Auburn University football coach Tommy Tuberville (top right), Alabama Secretary of State John Merrill (bottom left), and state Rep. Arnold Mooney (bottom right) are also running for the Republican nomination

Still it's unclear what role the president would play in the Republican primary should Sessions toss his hat in the ring.

In the 2017 Republican Senate primary, Trump supported Moore's opponent Luther Strange - even holding a rally for him - but it was Moore who ended up the nominee.

This time around, Moore has four other primary opponents - Rep. Bradley Byrne, former Auburn University football coach Tommy Tuberville, Alabama Secretary of State John Merrill, and state Rep. Arnold Mooney.

Sessions, if he ran, would be the sixth Republican in the primary.