Senate Appropriations Committee Chairman Thad Cochran (R-MS), citing his failing health, plans to resign from office by April 1, according to an announcement from his office.
"I regret my health has become an ongoing challenge," he said. "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."
Congress is scheduled to complete a fiscal year 2018 omnibus spending bill by March 23.
Cochran said he hoped for a "smooth transition" of political power in Mississippi. As for Washington, Sen. Richard Shelby (R-AL) is the next-most-senior Republican on the Senate Appropriations Committee after Cochran, who is the 10th-longest serving U.S. senator in history.