According to The Hill:
“[Senator] Cochran [of Mississippi], 80, in a statement said his health was an ‘ongoing challenge’ and he wanted to step down with enough time to ensure a ‘smooth transition’ to his successor.
‘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,’ Cochran said in a statement.
He will resign his seat on April 1, according to his office.”
Read the full article here.