President Donald Trump on Sunday claimed that retiring Sen. Bob Corker “begged” him for an endorsement and decided not to seek reelection when Trump declined to offer one — an aggressive attack on a still-powerful fellow Republican as the president struggles to jump-start his legislative agenda.

“Senator Bob Corker ‘begged’ me to endorse him for re-election in Tennessee. I said ‘NO’ and he dropped out (said he could not win without my endorsement),” Trump said in a series of tweets. “He also wanted to be Secretary of State, I said ‘NO THANKS.’ He is also largely responsible for the horrendous Iran Deal!”


He added, “Hence, I would fully expect Corker to be a negative voice and stand in the way of our great agenda. Didn't have the guts to run!”

Corker sarcastically fired back at Trump on Twitter on Sunday morning.

"It's a shame the White House has become an adult day care center. Someone obviously missed their shift this morning," the Tennessee Republican wrote.

While Corker didn't address Trump's claims, a source familiar with the matter said that when Trump and Corker met in September, the president said he would endorse and campaign for Corker if he ran again. Corker's office also explicitly rebutted the president's remarks later on Sunday by highlighting a newly disclosed conversation in which Trump tried to get Corker to reconsider his decision to leave the Senate after 2019.

"The president called Senator Corker on Monday afternoon and asked him to reconsider his decision not to seek reelection and reaffirmed that he would have endorsed him, as he has said many times," said Todd Womack, Corker's chief of staff.

Trump’s assault on a prominent Senate chairman could have dire implications for his agenda. Corker controls the confirmation of diplomatic nominees, and potentially a new secretary of state, if Rex Tillerson quits or is ousted.

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Furthermore, Senate Republicans control only 52 seats, and creating any new enemies in the conference could backfire later. Corker, for example, has already expressed distaste for his party’s zeal for tax cuts without making tough fiscal decisions.

Senate Republicans are privately worried that Trump could upset a tenuous budget deal with Corker that could hurt tax reform. Corker agreed to pass a budget expanding the deficit by $1.5 trillion to get to tax reform, but the Senate won’t vote on the budget until next week.

Trump’s claims come after Corker last week told reporters that some of the president’s advisers are helping control an otherwise chaotic situation.

"I think Secretary Tillerson, Secretary Mattis and chief of staff Kelly are those people that help separate our country from chaos," Corker said, referring to James Mattis and John Kelly.

The White House hit back at the Senate Foreign Relations chairman, with press secretary Sarah Huckabee Sanders saying it is the president who is holding back the chaos.

“Look, I think that the president is the one that’s keeping the world from chaos,” she said. “He has an incredible team around him that’s helping him lead that effort, and he’s had tremendous accomplishments on the international stage by working with allies and confronting enemies.”

Regarding Trump's Sunday morning knock on the Iran deal, Corker worked with Democrats to create a bill allowing Congress to review the pact to reduce Iran's nuclear capabilities. He was criticized by conservatives for creating a bill that made it impossible for the Senate to block the deal, but without his work with Democrats, Congress might have had no say whatsoever.

The president this week is expected to announce that he will decertify the Iran deal but that he'll kick the issue to Congress, which has control over sanctions.

Trump and Corker have had a publicly turbulent relationship. Corker appeared to irk Trump when he told reporters in August that “the president has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful.”

Trump jabbed back on Twitter a week later, writing, “Strange statement by Bob Corker considering that he is constantly asking me whether or not he should run again in '18. Tennessee not happy!”

Corker announced on Sept. 26 that he will retire from the Senate after two terms, shocking his colleagues.

“I just haven’t been able to bring myself to cross the line and say I was going to run. When I ran back in 2006, I told people I just couldn’t imagine serving more than two terms," Corker said in an interview at the time. “The thought of a third term just didn't feel like why I came here."

Seung Min Kim contributed to this report.