ON THE surface, the oil price war disrupting the global economy pits the world’s third-largest producer, Russia, against the second, Saudi Arabia. Make no mistake about it, however: The ultimate loser — and a probable intended target — is the world’s No. 1 crude producer, the United States. After years of stewing over his country’s loss of market share to the burgeoning U.S. shale industry, and the sanctions Washington has put on Russia’s oil industry in response to Moscow’s various abuses in international affairs, President Vladi­mir Putin has decided to fight back, in the form of unrestrained production that threatens to bankrupt many highly indebted U.S. companies.

The back story to Mr. Putin’s move is a stagnation in global consumption that has turned into an outright downturn due to the novel coronavirus. As de facto chief of the Organization of Petroleum Exporting Countries (OPEC), Saudi Arabia tried to persuade Mr. Putin to cut its production in tandem with the cartel, so as to prop up prices for them all. When he refused, Saudi Crown Prince Mohammed bin Salman countered by declaring his country would run its industry at maximum output for the foreseeable future. So far, Russia has not bowed to the pressure, partly because Moscow can balance its budget at a much lower price of oil than Saudi Arabia can, and partly because Mr. Putin smells an opportunity to get even with the United States. Russia’s oil-exporting partners Venezuela and Iran, already reeling from political unrest and the coronavirus, respectively, are likely to take politically destabilizing hits as a consequence, but apparently those are lower priorities for Moscow.

President Trump’s immediate response to all of this was to celebrate lower prices at the gas pump, which does indeed amount to a tax cut for U.S. consumers. The problem is that what the United States may gain in consumer purchasing power it will lose in financial-system instability, as the oil patch’s problems spread to their creditors and stockholders on Wall Street. There may be a double-edged impact on the climate, too, since greenhouse-gas emissions go up due to extra consumption of cheaper oil — and go down when production falls in U.S. oil fields. As both a colossal consumer and a colossal producer of oil for the foreseeable future, the United States is on both sides of the world’s biggest trade-off, both economically and environmentally. A tax on carbon would enable us to control climate risks no matter which way the markets move.

In geopolitical terms, Mr. Trump should be absorbing the lesson that Russia’s president is not a U.S. friend, actual or potential, but rather a despot willing to play hardball against this country’s vital interests. The Saudi crown prince, too, has shown himself to be an unreliable player on the international stage, putting the U.S. economy at risk when it suits him, despite the vast military assistance, and lavish rhetorical support, that the Trump administration has given his brutal regime. At a time when the whole world needs to pull together in the face of a global public health threat, these two men are destabilizing it for their own selfish ends.