CNN  — 

Jeff Sessions lost an Alabama Senate GOP primary runoff on Tuesday to former Auburn University football coach Tommy Tuberville, CNN projects, a major blow to the former attorney general who faced fierce opposition to his candidacy from President Donald Trump.

Tuberville, who was endorsed by the President, will now advance to the general election as the Republican candidate set to take on incumbent Alabama Democratic Sen. Doug Jones in November. Jones, who pulled off an upset in the deep red state in a 2017 special election, is widely viewed as the most vulnerable Senate Democrat facing reelection in 2020. As a result, the race is likely to be the Republican Party’s best pick-up opportunity of the cycle.

The outcome of the race marks a significant political defeat for Sessions, who had been fighting to reclaim a Senate seat that he had previously held.

Sessions was the first US senator to endorse Trump in the 2016 presidential race and was once a prominent figure in the Trump administration as the top official leading the Justice Department. But he fell out of favor with the President and became a target of Trump’s attacks after he recused himself while serving as attorney general from the FBI probe into Russian interference in the 2016 campaign.

Trump was quick to celebrate the victory for his candidate of choice on Tuesday night, tweeting, “Tommy Tuberville WON big against Jeff Sessions. Will be a GREAT Senator for the incredible people of Alabama. @DougJones is a terrible Senator who is just a Super Liberal puppet for Schumer & Pelosi. Represents Alabama poorly. On to November 3rd.”

Sessions offered his full support to his primary opponent in remarks to the media and supporters in Mobile, Alabama, on Tuesday night.

“He ran a really firm, solid race. He was focused on his goal, and on winning, he had a plan to do so,” Sessions said of Tuberville. “He is our Republican nominee, and we must stand behind him in November.”

Sessions also praised the Trump agenda, despite the President’s continued attacks against him.

“I think it’s time for this Republican Party to listen to the Donald Trump agenda,” he said.

Sessions also said in his remarks that he holds his “head high.”

“I leave elective office with my integrity intact. I feel good about it, I hold my head high,” he said. “I took the road less traveled, didn’t try to excuse myself or get in a fight or undermine the leader of our country, and the great work he has to do. That was an honorable path, I believe.”

The President endorsed Tuberville in March, calling him a “REAL LEADER who will never let MAGA/KAG, or our Country, down!” Trump went after Sessions over the past weekend, calling him “a disaster who has let us all down” in a tweet and saying, “We don’t want him back in Washington!”

Sessions pushed back, saying that Trump’s attack amounted to “juvenile insults.”

“I’ve taken the road less travelled. Not sought fame or fortune,” he tweeted in response. “My honor and integrity are far more important than these juvenile insults. Your scandal ridden candidate is too cowardly to debate. As you know, Alabama does not take orders from Washington.”

Sessions still commands a conservative following, but he had become an underdog in the fight for his old job after losing the support of the President.

Tuberville hammered Sessions over the decision to recuse himself from the Russia probe, saying in one ad that he “quit on the President” and “failed Alabama.” In response, Sessions touted his support of the President. In ads, Sessions has worn the red “Make America Great Again” hat. He has also defended his recusal, saying that he “protected the rule of law” and contributed to Trump’s “exoneration.”

Tuberville has repeated Trump’s slogans like “drain the swamp” and “build the wall” while reminding potential supporters of his winning tenure at Auburn from 1999 to 2008. Sessions, on the other hand, has tried to make an issue of Tuberville’s residency, calling him a “tourist” who moved from Florida to run for Senate and “an empty suit” who has hidden from the public.

The race advanced to a runoff after no candidate received more than 50% of the vote in a crowded GOP primary in March. Tuberville and Sessions made it to the runoff after ending up as the top two finishers with Tuberville narrowly edging out Sessions for first place.

Sessions, who had a reputation as a conservative Republican and immigration hardliner in Congress, had highlighted endorsements from former Republican Senate colleagues, including Richard Shelby, who serves as the senior senator from Alabama. But that appears to have been no match for having lost the President’s endorsement.

Trump overwhelmingly won the deep red state of Alabama in 2016. The President, however, may have hurt some of his credibility with Alabamans on Monday when he repeatedly referred to the University of Alabama’s head football coach Nick Saban by the wrong name during a call. As Trump praised Tuberville, he also lauded a football coach named Saban – just not the one who has secured five national championships for the state.

“Really successful coach,” Trump said of Tuberville. “Beat Alabama, like six in a row, but we won’t even mention that. As he said … because of that, maybe we got ‘em Lou Saban … And he’s great, Lou Saban, what a great job he’s done.”

While Trump was correct in pointing out that Tuberville led Auburn to six straight wins over Alabama between 2002 and 2007, he may have been referring to Lou Saban, the former head coach of the Buffalo Bills in the 1960s who died in 2009.

The ongoing coronavirus pandemic had also created a wild card factor in the race, making it difficult to predict what turnout would look like in advance. As a result of the outbreak, the date of the runoff was postponed from the end of March to July.

This story has been updated with additional developments Tuesday.

CNN’s Alex Rogers and Kaitlan Collins contributed to this report.