Biden gave Mohammed bin Salman a fist bump. His reward? A gut punch.

The move — with its intended boost in the price of oil — will give Russian President Vladimir Putin more revenue to fund his hideous war in Ukraine and to ease the pain of tough international sanctions. With Russian forces in retreat and fighting-age men fleeing the country to avoid being conscripted as cannon fodder, this is the best news Putin has had in months.

The world economy is still struggling to regain its footing after the disruptions and dislocations of the coronavirus pandemic. This decision by the Organization of the Petroleum Exporting Countries and its allies, including Russia, will not necessarily create an oil shock that sparks a global recession. But it makes that ugly scenario more likely.

And the production cut will likely raise gasoline prices just weeks before the midterm elections, wreaking havoc with U.S. domestic politics in a way certain to make Biden and the Democratic Party livid. If it’s an effort to slow the United States’ transition away from fossil fuels by electing Republicans, it’s a shortsighted and short-term one: Congress changes hands, but decisions such as California’s efforts to reshape the car market are here to stay.

Saudi Arabia is by far the biggest oil producer in OPEC, and thus calls the shots. Inside the kingdom, MBS, newly appointed prime minister, makes the decisions. How far can he press on — arrogant, brutal, autocratic, reckless, contemptuous of democratic values and innocent lives — before the United States says enough?

By unhappy coincidence, it was four years ago this week when Jamal Khashoggi, a dissident Saudi journalist who was a legal resident of the United States and wrote columns for The Post, was lured to the Saudi Consulate in Istanbul, murdered by a Saudi government hit squad and dismembered with a bone saw. The CIA concluded that MBS personally authorized the assassination. He denies involvement in the killing, bristles when asked about it — and most recently has used his new title to claim immunity in a lawsuit against him.

Donald Trump was president then, and he has a soft spot for the Saudis, who knew how to flatter his preening ego: Remember when he went to Riyadh, just four months after taking office, and laid his hands upon a glowing orb? Trump threw doubt on the CIA’s conclusion about Khashoggi, opposed congressional efforts to punish MBS and ignored atrocities the prince’s U.S.-equipped military was committing in Yemen. Trump preferred to boast about all the money U.S. firms were making from arms sales to the Saudis.

Biden decided to try to get the U.S.-Saudi relationship back on a track consistent with American values and interests — hence the visit and fist bump in July. This oil-production cut is the thanks he gets.

In the short term, the president has no choice but to do what he can to keep gas prices down. He could order the release of more oil from the Strategic Petroleum Reserve, perhaps in concert with other wealthy democracies. He is reportedly thinking about relaxing sanctions on Venezuela — run by another authoritarian thug, Nicolás Maduro — which would allow U.S. companies to bring more of that nation’s oil onto the market. Turning to the biggest potential immediate supplier of new oil — Iran — is not presently an option.

More broadly, Biden needs to realize that Saudi Arabia under MBS is more part of the problem than part of the solution — and to adjust U.S. policy accordingly.

He could throw the administration’s weight behind the bipartisan NOPEC bill — No Oil Producing and Exporting Cartels — that was passed by the Senate Judiciary Committee in May. The bill would revoke the sovereign immunity that protects OPEC members and allied oil-producing nations from antitrust lawsuits. The idea of such legislation has been around for years, and the Saudis have always lobbied as hard as they could to squash it.

Biden could also attach conditions to future deliveries of arms and spare parts to the Saudis. One of those conditions should be full and transparent accountability for Khashoggi’s murder. His family still doesn’t even know where his remains are.

Yes, these unsettled times require dealing with unsavory characters. But when one of them goes out of his way to hurt the United States, realpolitik means returning the favor.