EXCLUSIVE — Numerous Republican senators are throwing their support behind former colleague Jeff Sessions the day after he made a last-minute entrance into Alabama’s Senate race and are encouraging conservatives to do the same, as the former attorney general works to make peace with President Trump.

Fox News has learned that Alabama’s senior senator, Richard Shelby, is circulating an “open letter to conservatives” signed by at least 11 Republican senators who are endorsing Sessions’ candidacy. Sessions served in the Senate from 1997 to 2017 until he joined the Trump administration as attorney general.

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“Each of us has served in the United States Senate with Jeff Sessions,” the letter, obtained by Fox News, states. “We have seen him work diligently in the public eye and behind closed doors, when things were both good and bad, under stress and in success.”

The letter is signed by Shelby, Oklahoma Sen. Jim Inhofe, Kansas Sen. Pat Roberts, Wyoming Sen. Mike Enzi, Idaho Sen. Mike Crapo, Georgia Sen. Johnny Isakson, Wyoming Sen. John Barrasso, Missouri Sen. Roy Blunt, Arkansas Sen. John Boozman, Wisconsin Sen. Ron Johnson and Nebraska Sen. Deb Fischer.

“We know Jeff’s character and his temperament,” the letter reads. “We know his commitment to his principles. We know he is a man of his word. And we know he is devoted to serving the people of Alabama.

It adds: “We believe Jeff Sessions has more to offer his country, and we believe the United States Senate will be better with his experience and leadership.”

During a Thursday appearance on Fox News' "Tucker Carlson Tonight," Sessions announced plans to enter the race. Sessions, who resigned from the Justice Department a year ago amid public attacks from the president, was one of Trump’s most loyal and trusted advisers before their relationship soured over his recusal from the Russia investigation.

A major question hanging over Sessions’ entrance into the race is whether Trump -- who has remained popular in Alabama -- would take steps to thwart his bid.

But so far, Trump has not publicly attacked Sessions since he entered the race. Asked by reporters about Sessions on Friday, the president noted how Sessions had said “nice” things about him in his campaign announcement. He said he won’t campaign against Sessions but acknowledged the former attorney general will have “tough competition” in the GOP primary to take on incumbent Sen. Doug Jones, a Democrat.

Among the other Republicans running: U.S. Rep. Bradley Byrne, former Auburn football coach Tommy Tuberville, former Alabama Supreme Court chief justice Roy Moore, Alabama Secretary of State John Merrill, businessman Stanley Adair and State Rep. Arnold Mooney.

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One rival's campaign responded to the endorsements by accusing Sessions of enjoying support from the "establishment."

“After announcing his campaign from D.C., the swamp machine now rolls out support from establishment politicians. It’s time Jeff comes back to Alabama and realizes things aren’t quite how they once were,” said Lenze Morris, a spokesman for the Byrne campaign.

Other candidates have gone after Sessions by relitigating his history with Trump, with Tuberville tweeting this week, “As AG, he failed the President at his point of greatest need.” Tuberville's campaign released an ad Thursday highlighting Trump’s past comments calling Sessions a “total disaster” and “embarrassment” to Alabama.

The senators, though, in Friday’s letter vouched for him. Shelby said Sessions is “well-suited to return to his role as United States Senator for the state of Alabama, where I served with him for more than 20 years.” Inhofe said, “We need him back in the Senate.” Barrasso said Sessions “was unflinching ‘America First’ before it was cool.”