President Donald Trump, left, stands with Attorney General Jeff Sessions on December 15, 2017 in Quantico, Virginia, before participating in the FBI National Academy graduation ceremony.

President Donald Trump's campaign unloaded on Jeff Sessions, the former attorney general who is seeking his old U.S. Senate seat in Alabama, accusing him of attempting to mislead GOP voters into thinking the commander in chief supports him.

In a letter sent this week, the Trump campaign's chief operating officer, Michael Glassner, excoriated Sessions for claiming to supporters in mailers that he's "Trump's #1 Supporter."

"We only assume your campaign is doing this to confuse President Trump's loyal supporters in Alabama into believing the President supports your candidacy in the upcoming primary run-off election," Glassner said. "Nothing could be further from the truth."

Sessions is in a Republican primary battle in Alabama, as the GOP looks to take back the seat currently held by Democrat Doug Jones, who narrowly defeated disgraced former Judge Roy Moore in a 2017 special election. Jones is considered one of the most vulnerable senators up for election this year.

Sessions will face college football coach Tommy Tuberville in a runoff election for the GOP nomination in July. Trump has endorsed Tuberville.

Trump fired Sessions from leading the Justice Department in November 2018 after he repeatedly lambasted the former Alabama lawmaker for recusing himself from overseeing special counsel Robert Mueller's investigation into Russian interference during the 2016 election.

Sessions was one of Trump's earliest supporters in the 2016 presidential campaign. "Devil's Bargain," a book written by reporter Josh Green, reports that Sessions was convinced to back Trump by former White House chief strategist Steve Bannon.