In recent years, Mr. McConnell’s longstanding commitment to civil rights legislation has come into conflict with his party’s push for state-imposed limits on early voting, voter identification requirements and other measures that Democrats say are intended to disenfranchise minorities.

Eyes will now turn to Mr. McConnell, an early voice calling for the removal of the Confederate battle flag from the South Carolina capitol, after a major skirmish in the House this week over the use of the flag on federal land. “One thing I am not in favor of erasing is our history,” he said, referring to the removal of statues, not the House debate on the flag. “The Civil War was a part of our history and there were actually good people on both sides of that war.”

The tension can be seen in his own ambivalence about changes to civil rights laws proposed by some members of Congress, including measures that would bring back federal oversight of elections in some states.

But Mr. McConnell’s interest in race issues was inspired by his upbringing in Kentucky by parents who opposed segregation. It was fermented on the campus of the University of Louisville, where he encouraged students to march with the Rev. Dr. Martin Luther King Jr. It was reinforced by his internship in the office of Senator John Sherman Cooper, a Kentucky Republican who helped break the Southern-led filibuster of the Civil Rights Act of 1964.

It also surfaced during his first term in the Senate, when Mr. McConnell’s vote helped Congress override President Ronald Reagan’s veto of a measure imposing sanctions on South Africa during apartheid, and has persisted through his years in the United States Capitol, most recently last month, when Mr. McConnell stood before reporters and said that a statue of Jefferson Davis, the president of the Confederacy, should be removed from Kentucky’s Capitol.