Sen. Thad Cochran (R-Miss) will resign from the Senate on April 1, ending a four-decade congressional career and triggering a fall election that could carve new divisions in the Republican Party and endanger the GOP Senate majority. Cochran, 80, has been suffering from health problems in recent months. "I regret that my health has become an ongoing challenge," he said in a statement. "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 US Senate." When he steps down, chairmanship of the Appropriations Committee is expected to pass to Sen. Richard Shelby (R-Ala), who is next in the line of seniority.