They unsuccessfully tried this strategy in 2012, when Mr. McConnell blockaded the nomination of Judge Merrick B. Garland to the Supreme Court, maintaining that voters should decide who would name the next justice when they picked a president that November. They tried and failed again late last year, weeks before a presidential election, when the death of Justice Ruth Bader Ginsburg opened a Supreme Court seat for Judge Amy Coney Barrett to fill, no matter what voters had to say a month and a half later.

Now, with a potential government default weeks away, Democrats are again demanding that Mr. McConnell back down — this time from his vow to lead Republicans in opposition to raising the statutory limit on the Treasury Department’s authority to borrow…

A default would be unprecedented, and it could lead to a far-reaching financial crisis — or at least a crisis in confidence for the governments, banks and other creditors that keep the federal government afloat by purchasing its bonds and notes.

But Mr. McConnell is adamant that if Democrats insist on spending trillions of dollars on infrastructure, climate change and social welfare, they must bear exclusive responsibility for raising the borrowing limit. A purely Democratic vote to raise the debt ceiling, of course, would fortify Republican political attacks on what they characterize as an out-of-control, “socialist” party.