Senators are scheduled to be on a break from Washington for the next two weeks, but they have left behind a rearguard to keep the chamber running on low gear, denying President Obama a chance to install his Supreme Court nominee.

It’s part of Republicans’ vow to do everything to keep Mr. Obama from replacing the late Justice Antonin Scalia, whose death last month left the court divided 4-4, and left Democrats salivating over the opportunity to replace the conservative Scalia with a liberal.

Mr. Obama last week nominated Judge Merrick Garland, an appeals court judge in the District of Columbia, to fill Scalia’s seat.

Judge Garland has received near universal praise for his qualifications and temperament.

Still some advocacy groups important to Republicans, such as the National Rifle Association and the National Federation of Independent Business, have given him low marks for rulings.

Republican leaders didn’t budge in their vow to deny any Obama nominee a hearing, much less a vote, saying the responsibility for picking a replacement should rest with the next president.

Senate Majority Leader Mitch McConnell, Kentucky Republican, flatly ruled out any action again Sunday, saying Judge Garland won’t get a floor vote.

“The schedule in the Senate is set by the majority leader. And most of my members are very comfortable with letting the American people make this decision by electing the next president, who will fill this vacancy next year,” Mr. McConnell told ABC’s “This Week” program.

Part of that strategy is denying Mr. Obama the opening to make a recess appointment.

Senators have scheduled pro forma sessions to meet a couple of times a week, with no business scheduled, specifically to deny Mr. Obama that chance. Under Senate rules, that is enough to prevent the constitutional trigger that would let Mr. Obama deem the Senate in recess and make an appointment without them.

“It’s very smart for the Senate to take every conceivable precaution to ensure the president doesn’t try to recess appoint his nominee,” said Brian Rogers at America Rising Squared, a conservative pressure group.

When the Scalia seat opened last month, the Senate had just entered a full recess for Presidents Day, and some scholars argued that Mr. Obama could have pulled the trigger on an appointment then. Thanks to Republican tactics, that avenue is likely closed for good.

Senate Minority Leader Harry Reid, Nevada Democrat, predicted that Mr. McConnell will eventually cave when pressure grows too high on his fellow Republicans.

“I don’t know why McConnell’s done this to his senators,” Mr. Reid told NBC’s “Meet the Press” on Sunday. “He’s marching them over a cliff, and I don’t think they’re going to go.”

He and other Democrats said they saw the first signs of cracks in the blockade last week when several Republican senators said they would consider confirming Judge Garland in a lame-duck session late this year if Hillary Clinton wins the presidential election. But Mr. McConnell ruled out even that possibility, saying the next president, no matter who wins the election, will fill the seat.

With Washington going on Easter break, both sides are increasing their efforts to defend their stances to voters back home.

The Judicial Crisis Network, a conservative group, has vowed to spend $2 million to defend a couple of Republican senators who are balking at Mr. Obama’s pick and to go after several Democrats, demanding that they oppose the president’s effort to shift the court to the left.

Liberal groups, meanwhile, are rallying editorial pages back home, arguing that by refusing to vote on Judge Garland, Republicans in the Senate are flouting their constitutional responsibilities. Polling suggests that Democrats are winning the debate, with even Republican voters saying the Senate should hold hearings on Judge Garland.

The Congressional Research Service said the Scalia vacancy is unique in modern American political history. “It is the only vacancy that has existed during the eighth, and final, year of a presidency that also arose during the eighth year itself,” the organization said in a legal memo last week.

Several seats have come open in the final year of a president’s term, but in each of those instances it was when a president was running for re-election.

The Congressional Research Service said there has been one recess appointment of a Supreme Court justice during a presidential election year, when President Eisenhower installed William J. Brennan in 1956. Brennan was confirmed to a complete term in 1957.

Ironically, it was Mr. Obama’s own aggressive tactics that left him vulnerable to Republicans’ pro forma strategy to deny him recess appointment powers.

In 2012, Mr. Obama issued a slate of recess appointments even while the Senate was meeting every few days in pro forma sessions. He said pro forma sessions weren’t really meetings, so he was justified in his move.

But the Supreme Court, in a unanimous 2014 ruling, held that Mr. Obama violated the Constitution in making those appointments. The justices said a recess had to be at least three days, and in all but emergencies needed to be 10 days.

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