It’s not just left-leaning voters that Republicans are willing to disenfranchise to maintain power.

Now that challengers to President Donald Trump have begun to emerge from within his own party, at least four states are taking steps to cancel their 2020 GOP primaries and caucuses.

It’s a stunning admission of a) the party’s willingness to subvert basic tenets of democracy; b) the dismissiveness with which the party is willing to treat its own voters; and c) the weakness of the party’s erstwhile leader.

It should also put to rest any doubts that concerted GOP efforts nationwide to purge registration rolls, tighten voting requirements and diminish the number of polling stations have anything whatsoever to do with combating the nonexistent threat of voter fraud.

Republican party leaders in South Carolina and Kansas voted to cancel their 2020 presidential primaries. Officials in at least two other states — Nevada and Arizona — are contemplating doing the same. The moves are intended to show support for the president in the wake of several declared or contemplated primary challenges.

Former Massachusetts Gov. William Weld, former Rep. Joe Walsh and South Carolina governor and congressman Mark Sanford are in the race and former Rep. Mo Brooks also has discussed a run.

All deserve the opportunity to make their case to Republican voters. The days of backroom candidate selections were supposed to have gone the way of smoke-filled rooms.

State-level party leaders are hearing none of that, however. They may have saddled themselves with a lazy, self-obsessed standard-bearer who’s more interested in petty spats than the public good, but he’s doing their bidding in terms of tax cuts and federal judges. So they’re evidently going to do everything they can to drag him across the finish line.

It’s nothing if not ironic: After whining for much of the 2016 campaign that the election was rigged, Trump sits back while his party rigs the 2020 election in his favor.

Funny thing, though: The number of Republicans — voters, lawmakers, administrators — who have been willing to remain silent while the president and his administration run roughshod over mores, protocols, policies and even laws has been astonishing. From defending dimwitted if harmless misstatements about the path of a hurricane to refusing comment about suspicious changes in international military routes that benefit the president financially, the wagons have been circling furiously.

So instead we get lame justifications. South Carolina GOP Chairman Drew McKissick notes that Republicans in his state cancelled primaries in 1984 and 2004, and that Democrats did the same in 1996 and 2012.

Of course, Ronald Reagan (1984), Barrack Obama (2012), George W. Bush (2004) and Bill Clinton (1996) didn’t face a serious primary challenge, so the argument is moot.

Trump, on the other hand, is a divisive figure who has done little to reach out beyond his faithful base either within or outside GOP circles. His vision, if he has one, remains a mystery more than two and half years into his presidency. His reckless decisions and insulting comments routinely diminish the office and the nation.

In short, he deserves to be challenged, not protected. He should be required to defend his record and spell out his agenda — not just in a general election, but among challengers within his own party. Registered Republicans deserve to decide on their party’s candidate for the nation’s highest office.

The Republican Party has been demonstrating for years its disregard for fair general elections. Now, they’re taking their “undemocratic BS” one step further. Republican voters should refuse to stand for it.