(AP) — Republican Sen. Thad Cochran of Mississippi has given a farewell speech in the U.S. Senate, where he’s the longest-serving current member of Congress.

The 80-year-old Cochran is retiring April 1 because of poor health. He says he’s “optimistic about the future of our great nation.”

Cochran served in the House six years before joining the Senate in 1978.

Colleagues paid tribute to Cochran on Thursday at the U.S. Capitol, repeatedly praising the Senate Appropriations Committee chairman for being civil while working across party lines.

Senate Majority Leader Mitch McConnell of Kentucky says Cochran “wrote the book on composure under pressure.”