President Trump endorsed ex-Auburn football coach Tommy Tuberville over former U.S. Attorney General and erstwhile U.S. Sen. Jeff Sessions, tweeting that Tuberville “will be a great senator for the people of Alabama.”

Tommy Tuberville (@TTuberville) is running for the U.S. Senate from the Great State of Alabama. Tommy was a terrific head football coach at Auburn University. He is a REAL LEADER who will never let MAGA/KAG, or our Country, down! Tommy will protect your Second Amendment.... — Donald J. Trump (@realDonaldTrump) March 11, 2020

Tuberville and Sessions will square off in a March 31 runoff election after they were the top two votegetters in the Republican Senate primary on March 3.

Trump’s tweet was a blow to Sessions, who has campaigned on being the candidate most aligned with the president’s values, pointing out that he was the first sitting senator to back then-candidate Trump’s campaign. But the former attorney general stepped down from his Trump administration post after the president was angering over Sessions recusing himself from the Russia investigation, which paved the wave for the special counsel probe led by former FBI Director Robert Mueller.

Conversely, Trump’s endorsement is a boon to Tuberville’s campaign and came hours after a new poll showed the football coach with a double-digit lead over Sessions.

Sessions’ ties to Trump go back to the summer of 2015, when the then-senator appeared at a Trump rally in Mobile and donned the campaign’s iconic red “Make America Great Again” hats. Sessions endorsed Trump at a rally in February 2016.

Trump returned the favor by tapping Sessions as his attorney general, although the two had a strained relationship over the Russia investigation.

The president even went so far as mocking Sessions’ second-place finish in last week’s primary, tweeting: “This is what happens to someone who loyally gets appointed Attorney General of the United States & then doesn’t have the wisdom or courage to stare down & end the phony Russia Witch Hunt. Recuses himself on FIRST DAY in office, and the Mueller Scam begins!”

Support for Trump has been the defining issue of the Republican primary campaign, with Tuberville attacking Sessions for letting the president down over his recusal in the Russia probe while Sessions has counter-punched by using snippets of video of Tuberville saying he was “pissed off at Donald Trump” over the administration’s response to veteran’s healthcare issues.

The attacks from both campaigns have largely been argued through campaign ads and social media as no debates are scheduled between Tuberville and Sessions.

Sessions has challenged Tuberville to debate -- a strategy that the former senator strayed from in the runup to the primary. Tuberville’s campaign said a debate is not doable with the runoff election three weeks away.