Washington (CNN) President Donald Trump said Monday he supports Mitt Romney's bid for the US Senate from Utah, endorsing a former rival and major figure within the Republican Party.

".@MittRomney has announced he is running for the Senate from the wonderful State of Utah. He will make a great Senator and worthy successor to @OrrinHatch, and has my full support and endorsement!" Trump tweeted Monday evening.

.@MittRomney has announced he is running for the Senate from the wonderful State of Utah. He will make a great Senator and worthy successor to @OrrinHatch, and has my full support and endorsement! — Donald J. Trump (@realDonaldTrump) February 20, 2018

The endorsement marked the latest chapter in an at-times tumultuous relationship. Romney was among the top Republican critics of Trump's behavior during the 2016 campaign, and Trump fired back in return, mocking Romney for his loss in the 2012 presidential election.

Romney responded later Monday night, tweeting, "Thank you Mr. President for the support. I hope that over the course of the campaign I also earn the support and endorsement of the people of Utah."

The former Massachusetts governor announced February 16 that he would run for the Senate seat currently occupied by GOP Sen. Orrin Hatch, who said earlier this year that he would retire, and thereby cleared the path for Romney in the heavily Republican state.

Thank you Mr. President for the support. I hope that over the course of the campaign I also earn the support and endorsement of the people of Utah. — Mitt Romney (@MittRomney) February 20, 2018

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