In recent months, Rubio quietly withdrew his support for the nomination of a Miami judge who would have been the first openly gay black man on the federal bench. Although he initially backed William Thomas for a seat on the U.S. District Court for the Southern District of Florida last year, a spokeswoman said further review raised concerns about the judge’s “judicial temperament and his willingness to impose appropriate criminal sentences” in two cases.

Legal and civil rights groups have alleged Rubio’s motives are political. They note that in one case, a hit-and-run in which Rubio thought the sentence was too lenient, the lead prosecutor and an administrative judge wrote the senator saying Thomas had acted fairly.

“To me, that would not be a basis to prevent the confirmation process from going forward,” said Yolanda Strader, president of Miami’s largest association for black lawyers.

While some of Rubio’s actions could alienate moderates and independents in a general election, they have not gone unnoticed in the early-voting states that play an outsized role in picking presidential nominees. There, social issues are often at the top of Republicans’ concerns.