Sen. Mark Pryor, D-Ark., recently found out how fickle his former allies in the gun lobby can be.

Last year, Pryor was one of only four Democrats in the Senate to buck popular opinion and vote against the Manchin-Toomey amendment that would have closed loopholes in the gun background-check system.

To the consternation of his supporters, Pryor voted “no” on Manchin-Toomey because he figured a vote against the gun lobby — even on something as middle-of-the-road as background checks — would make him vulnerable in his re-election race.

At first the National Rifle Association responded favorably to Pryor’s gambit, running radio ads thanking him for his vote. Then last month, the NRA launched a TV ad campaign in support of Pryor’s opponent, Rep. Tom Cotton, R-Ark. To date, the NRA has spent more than $2 million backing Cotton.

For all his maneuvering, Pryor ended up in the gun lobby’s crosshairs anyway. And it’s clear now that his vote against Manchin-Toomey was more naïve than it was calculating.

If Pryor loses — and recent polls showed his opponent leading by a slight margin — pundits will point to a number of contributing factors.

But regardless of whether he wins, Pryor’s predicament is an object lesson in gun politics.

When it comes to gun issues, candidates have two options now.

One is to support reasonable gun laws. It’s not controversial and it’s not complicated. You can be for both the Second Amendment and for public safety measures that help save lives.

Or, you can follow the Pryor playbook. You can try to court the gun lobby.

You can do what Pryor did, and go against the will of the 84 percent of Arkansans who supported the background checks bill — and the 92 percent of Americans who want to close loopholes in the law and require background checks for all gun buyers.

Like Pryor, you can parrot the NRA- approved line about finding “real solutions” to gun violence instead. You can claim that a lack of mental health services is “the real issue” — and ignore the reality that today felons and domestic abusers are buying guns at gun shows and online, no questions asked.

You can try to toe the NRA line. And like Pryor, you’ll lose the gun lobby’s support anyway — because evidently, a vote against background checks isn’t enough.

It’s not enough, because there’s always a candidate out there willing to do a little more to earn the NRA’s endorsement.

Tom Cotton, the NRA’s preference in Arkansas, has co-sponsored a concealed carry reciprocity bill, long the gun lobby’s top legislative priority.

So unless you’re willing to vote against background checks — and for concealed carry reciprocity and an ideology of more guns everywhere (schools, bars, airports), regardless of who’s buying them (stalkers, domestic abusers, terrorists), then you can’t count on the gun lobby’s support.

Sen. Mark Begich, D-Alaska, learned this the hard way, too.

Begich, a Democrat, voted “no” on Manchin-Toomey. Before that, when he was mayor of Anchorage, he joined and then — under pressure and with higher office in sight — resigned from the Mayors Against Illegal Guns coalition, citing the NRA’s talking points chapter and verse.

Begich’s reward? The NRA is sitting out his tight re-election race.

Recently, an NRA spokesperson said Begich’s votes for two Supreme Court justices will keep the group from endorsing him. It won’t endorse the Republican challenger either, but now Begich’s opponent is running an ad questioning the senator’s support for Second Amendment rights.

As it’s shown in Arkansas and Alaska, the gun lobby isn’t interested in aiding anyone besides its most dedicated zealots. When they’re facing votes on gun issues, Democrats especially shouldn’t kid themselves.

The NRA doesn’t do nuance. So for lawmakers, the choice is clear.

By supporting sensible gun policies, lawmakers won’t only be doing the right thing. They’ll also likely find that come election time, authenticity and common sense play better than cold calculation.

In other words, by standing up for policies that a vast majority of the American public supports, candidates are likely to impress voters enough to keep their jobs.

We’ll see if Pryor and Begich get to keep theirs.

John Feinblatt is president of Everytown for Gun Safety.