Democrats accused Mitch McConnell, the Senate majority leader, of hypocrisy on Tuesday after he said Republicans would confirm a justice to the Supreme Court if a seat opened up amid the election campaign in 2020, even after denying President Barack Obama a similar opportunity in 2016.
The senator made the remarks at a Chamber of Commerce event in Paducah, Ky., after an audience member asked what Senate Republicans would do if a Supreme Court justice died next year.
“Oh, we’d fill it,” he responded with a grin, prompting laughter from the audience.
When Mr. McConnell denied Judge Merrick B. Garland, Mr. Obama’s choice to fill a Supreme Court vacancy, a hearing in 2016, the senator cited election-year “tradition” going back to 1880 in keeping the seat open until a new president could be inaugurated.
Mr. McConnell’s remark on Tuesday made it clear that was not his only consideration. It was the most direct acknowledgment yet that Senate Republicans would treat a judge nominated by a Republican president differently from one nominated by a Democratic president.
After successfully keeping Mr. Garland off the court, Republicans went on to cement a conservative majority when Judge Neil M. Gorsuch, who was nominated by President Trump, was confirmed in April 2017. Mr. Trump added another conservative, Judge Brett M. Kavanaugh, to the court last year.
Mr. McConnell’s most common explanation for blocking Mr. Garland — that a new president should get to fill a Supreme Court opening that occurs close to an election — struck Democrats as disingenuous at the time, and many said it looked even more so after Tuesday’s comments.
“Senator McConnell is a hypocrite,” Chuck Schumer, the Senate minority leader, said on Twitter.
Julián Castro, a Democratic presidential candidate, said on Twitter that Mr. McConnell’s “shamelessness at stealing a Supreme Court seat is appalling.”
In the past year, as bitterness lingered among Democrats over the episode, Mr. McConnell tried to reframe his reasoning to focus on the split control of government at the time.
In 2016, Democrats held the White House while Republicans controlled the Senate, whereas Republicans now control both. He offered that explanation on “Fox News Sunday” in October, and David Popp, a spokesman for Mr. McConnell, cited the same explanation on CNN on Tuesday.
Mr. McConnell did occasionally mention the divided government in 2016, but it was not his chief argument at the time and was frequently omitted from his remarks. Last October, when asked about the issue on CBS’ “Face the Nation,” he said, “What I did was entirely consistent with what the history of the Senate’s been in that situation going back to 1880.”
The last time a Republican-led Senate confirmed a nominee put forth by a Democratic president was 1895, when it confirmed Rufus W. Peckham after he was nominated by Grover Cleveland. Since then, Democratic-controlled Senates have approved 13 nominees by Republican presidents.
Before 2016, there had been just seven election-year confirmation battles since the beginning of the 20th century. In the most recent case, Anthony M. Kennedy, who was appointed by President Ronald Reagan, was confirmed in 1988 by a Democratic Senate in a 97-to-0 vote after a grueling seven-month process.
The only time a Senate has failed to confirm a nominee in an election year was 1968, when the nomination of Abe Fortas was withdrawn. Both the Senate and the White House were controlled by Democrats at the time.
On the current court, two of the justices are in their 80s, and one of them, Justice Ruth Bader Ginsburg, 86, has suffered a series of health problems.
In Mr. McConnell’s remarks to the Paducah Chamber of Commerce, in his home state of Kentucky, he said that legislative accomplishments like tax reform could be undone by future administrations, but that Supreme Court confirmations could have a more lasting impact.
“What can’t be undone is a lifetime appointment to a young man or woman who believes in the quaint notion that the job of a judge is to follow the law,” he said. “That’s the most important thing we’ve done for the country, which cannot be undone.”