We all know that President Trump is a sore loser — and even a sore winner — with a tenuous grip on reality. He screamed “fraud” after losing the 2016 Iowa caucuses to Sen. Ted Cruz (R-Tex.). He made similar claims when he lost the popular vote to Hillary Clinton in 2016. He even formed a commission to investigate supposed election fraud in 2016; it disbanded after finding none.

So it was inevitable that if Trump lost the 2020 election that he would allege that he had been cheated of his rightful victory even without any evidence of any cheating. What was not inevitable was that the leaders of the Republican Party would support his claims and that Attorney General William P. Barr would authorize prosecutors to proceed in investigating largely nonexistent voter fraud. (Richard Pilger, a well-respected career lawyer who was head of the Justice Department’s Election Crimes Branch, resigned in protest over Barr’s decision.)

The cynicism is endless, appalling and corrosive. Senior Republicans know that Trump lost and that the vote was free and fair. After all, many of them won reelection on the same ballots that were cast to elect Joe Biden. How could part of the ballot be fair and part fraudulent?

Sen. Christopher A. Coons (D-Del.) said that several of his Republican colleagues have told him in private: “Please convey my well wishes to the president-elect, but I can’t say that publicly yet.” The news is full of reports that Trump retainers and family members — even Jared Kushner and Melania Trump — are struggling to get him to accept the reality that he lost. And yet Republicans keep the charade going because their leader is too much of a “snowflake” to admit that he was just repudiated by more than 76 million Americans.

One senior Republican official told The Post: “What is the downside for humoring him for this little bit of time? No one seriously thinks the results will change.” It is hard to imagine a better encapsulation of how feckless and dangerous the Republican Party has become. What’s the downside? Only the undermining of our democracy.

Many countries have elections. But only in functioning democracies do losers recognize the result and transfer power to the winners. “Graceful concessions by losing candidates constitute a sort of glue that holds the polity together, providing a cohesion that is lacking in less-well-established democracies,” writes Shaun Bowler, a political scientist who is a co-author of “Losers’ Consent: Elections and Democratic Legitimacy.”

By not conceding the election — even though Joe Biden appears to have won the same number of electoral college votes as Trump did in 2016 along with a larger share of the popular vote than any challenger since 1932 — Republicans are dissolving the “glue” that holds our republic together. You can see the damage being done in a new Politico-Morning Consult poll. It found that the number of Republicans who now say they don’t believe the 2020 election was free and fair has doubled since the election — from 35 percent before the vote to 70 percent today.