Mitch McConnell, the Senate majority leader, has had a rough couple of weeks. Yet, however many setbacks he might suffer over health care reform or other parts of the Republican agenda, he knows he has already won the biggest fight of all: the theft of a Supreme Court seat from President Obama, the installation of Justice Neil Gorsuch and the preservation of the court’s conservative majority for years to come.

“One of my proudest moments was when I looked at Barack Obama in the eye and I said, ‘Mr. President, you will not fill this Supreme Court vacancy,’ ” Mr. McConnell told a political gathering in Kentucky last summer.

With this audacious pledge — made only hours after news of Justice Antonin Scalia’s death on Feb. 13, 2016, reached the public — Mr. McConnell demolished longstanding Senate tradition and denied a vote to one of the most well-qualified nominees ever: Merrick Garland, the veteran federal appellate judge Mr. Obama had chosen to replace Justice Scalia.

As the court’s term ended last week in a flurry of high-profile opinions and orders, it was clear that Mr. McConnell’s gambit had paid off in the extreme. It’s risky to read too much into a justice’s early opinions, but Justice Gorsuch, who was confirmed less than three months ago, has already staked his claim as one of the most conservative members of the court.