Sen. Jeff Merkley (D-OR) came out against Rahm Emanuel’s ambassadorship Wednesday, putting the former Chicago mayor’s nomination to the Japan post in doubt as his civil rights record comes into focus. “Black Lives Matter,” Merkley said in a statement. “I have carefully considered Mayor Emanuel’s record—and the input of civil rights leaders, criminal justice experts, and local elected officials who have reached out to the Senate to weigh in—and I have reached the decision that I cannot support his nomination to serve as a U.S. Ambassador.” Emanuel has come under fire for his role in covering up the 2014 police killing of Black teenager Laquan McDonald, drawing the ire of progressives both at home in Chicago and in the House of Representatives.

The nomination, which has not been advanced out of the Senate Foreign Relations Committee, has drawn some Republican support, though two Senate progressives—Sens. Elizabeth Warren (D-MA) and Bernie Sanders (I-VT)—have not commented on how they’ll vote if the nomination reaches the floor.