Sen. Thad Cochran of Mississippi says he will retire in April due to health issues

Sen. Thad Cochran of Mississippi announced Monday that he will resign effective April 1.

Cochran, who has appeared increasingly feeble in recent years, said in a statement released by his office that his health “has become an ongoing challenge.”

“I intend to fulfill my responsibilities and commitments to the people of Mississippi and the Senate through the completion of the 2018 appropriations cycle, after which I will formally retire from the U.S. Senate,” said Cochran, who is 80.

The retirement underscores the tenuous nature of Republican control of the Senate during the Trump administration, when their narrow margin has complicated efforts to repeal President Obama’s healthcare plan, among other measures. Already, Vice President Mike Pence has had to step in at times to break ties.

After the December election of Alabama Democrat Doug Jones, Republicans effectively held a 51-49 advantage. But Sen. John McCain of Arizona has been missing from the Senate for months as he fights brain cancer, denying the majority his vote.

Under Mississippi rules, Gov. Phil Bryant will appoint an interim senator, who will serve in the strongly Republican state until a special election in November. The winner will hold the seat until 2020, when Cochran’s term would have ended. The second Mississippi senator, Republican Roger Wicker, will also be on the ballot in November.

The senator missed weeks of work last fall because of recurring medical issues. Even before that, he had curbed his public statements and meetings, amid reported incidents of confusion. He served in the House for five years before winning his Senate seat in 1978.

His stiffest challenge came in 2014, when a tea party Republican, Chris McDaniel, finished ahead of Cochran in the primary, only to lose in the general election after establishment Republicans and Democrats rallied to his side.

McDaniel announced last week that he planned to run against Wicker in November.