Russian President Vladimir Putin said on Friday that he will not bow to new U.S. sanctions but conceded “some losses are expected.” That is an understatement. The sanctions—the first in President Donald Trump’s second term—will hit Russia’s war budget by imposing a total embargo against Russian energy giants Rosneft and Lukoil.

It’s a tough blow. But enforcement will be key. Russia will try to sell oil under the table, using its shadow fleet of tankers and various cutouts: middlemen, front and unsanctioned companies, fake documents, and more. The U.S. will have to put its back into rooting out underground Russia’s oil networks.

That means slapping sanctions on the entire Russian shadow fleet of tankers and targeting ports, fueling sources, and other services they rely on. The White House could also slap sanctions against third countries that buy Russian oil from any source. They could waive these sanctions if the purchasing countries reduce volumes every six months; a sensible........

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