WASHINGTON — The Senate majority leader, Mitch McConnell, on Sunday dismissed the possibility of Republicans considering President Obama’s Supreme Court nominee after the November election, even if a Democrat were elected president or Republicans lost their majority.

In doing so, Mr. McConnell tried to shut the door on a scenario that some Republicans in the Senate have said could allow them to prevent a more liberal jurist than Mr. Obama’s nominee, Judge Merrick B. Garland, from reaching the court, should a Democrat win the White House.

“That’s not going to happen,” Mr. McConnell said of such an arrangement on “Fox News Sunday.” “The principle is the same. Whether it’s before the election or after the election. The principle is the American people are choosing their next president, and their next president should pick this Supreme Court nominee.”

But Mr. McConnell also offered a qualitative assessment of Judge Garland that, until now, he had said was unnecessary until a new president was sworn in. He suggested that Republicans had reason to oppose Judge Garland based on his judicial philosophy.