...The pivotal moment came in February 2016 when Supreme Court justice Antonin Scalia, the court's leading conservative, suddenly died. If Barack Obama had been able to replace him he would have created a 5-4 progressive majority on the country's most powerful court.
Instead, McConnell declared that he would not allow confirmation hearings for any Supreme Court nominee until after the presidential election - a unprecedented move in US history.
"He came up with the idea very quickly, within hours of Scalia passing away, and he implemented it brilliantly," says Curt Levey, president of conservative advocacy group the Committee for Justice. "It was very impressive..."