WASHINGTON — President Trump fired back at criticism from a Republican senator on Sunday, saying Sen. Bob Corker was a "negative voice" in the Senate and was responsible for the "horrendous" Iran nuclear deal.

Trump's Sunday morning Twitter salvo followed weeks of increasing criticism of the president by Corker, who announced last week that he would not run for re-election in 2018.

"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!

"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 fired back on Twitter later Sunday morning: "It's a shame the White House has become an adult day care center. Someone obviously missed their shift this morning."

Corker, the chairman of the Senate Foreign Relations Committee, was the architect of a procedural bill that allowed the Iran nuclear deal to proceed last year. Trump is facing an Oct. 15 deadline to recertify that deal, in which the U.S. and five other world powers agreed to ease sanctions on Iran in exchange for international monitoring of Iran's nuclear program.

Trump and Corker have been feuding since August, when Corker questioned Trump's competence to lead. He stood behind those comments last week, adding that Secretary of Defense James Mattis and Secretary of State Rex Tillerson were "people that help separate our country from chaos" — implicitly identifying Trump as the source of that chaos.

Trump's response followed a pattern of rebuking former allies by noting that he rejected their pleas for help.

In July, he accused MSNBC talkers Joe Scarborough and Mike Brzezinski of turning on him after he rebuffed them at his Mar-a-Lago resort. And when CEOs started to resign en masse from presidential commissions over his response to a white nationalist rally in Charlottesville, he said it was because he had lectured them on moving jobs overseas.