RUTHFULLY YOURS

Here’s what we know. Several hundred men and materiel advanced on a U.S. Special Forces base near Deir al-Zour on the night of Feb. 7-8. Pentagon spokeswoman Dana White confirmed soon afterward that the “battalion-sized unit formation” was “supported by artillery, tanks, multiple-launch rocket systems and mortars.” U.S. forces responded in self-defense “with a combination of air and artillery strikes.”

Ms. White wouldn’t confirm how many attackers were killed or who was fighting, though the U.S. had “observed” the military buildup for a week. Defense Secretary James Mattis called the confrontation “perplexing,” adding that “I have no idea why they would attack there, the forces were known to be there, obviously the Russians knew.” He’s referring to the U.S.-Russia “deconfliction” agreement in which the Russians agreed to stay west of the Euphrates River.

Now we’re learning that Russian fighters were killed in the attack, and Lebanese Hezbollah was also involved. The Kremlin has tried to cover up the deaths, but that’s getting harder as the body bags come home and Russian social media spread the word. The Foreign Ministry finally admitted Tuesday that “several dozen” Russians were killed or wounded but claimed that “Russian service members did not take part in any capacity and Russian military equipment was not used.”

That depends on how you define “Russian military.” Evidence is growing that the attack was orchestrated by Yevgeny Prigozhin, the Russian oligarch who does much of Mr. Putin’s dirty work. His businesses include the Internet Research Agency, a media operation indicted by a federal grand jury last week for meddling in the 2016 U.S. election.

Mr. Putin has a history of using mercenaries in Crimea and southern Ukraine, the better to preserve deniability if something goes wrong. The Obama Administration blacklisted Mr. Prigozhin in 2016 for supporting Russia’s Ukraine invasion, and in June the Trump Administration sanctioned Dmitry Utkin, a former Russian intelligence officer associated with Mr. Prigozhin’s Wagner Group of mercenaries.

Wagner has been fighting in Syria since 2015, according to the Institute for the Study of War’s Bradley Hanlon, including campaigns to retake oil-rich areas. Mr. Putin has been doling out contracts tied to oil and mining to mercenaries in Syria, including to Mr. Prigozhin.

The Washington Post reported Thursday, citing intelligence sources, that Mr. Prigozhin had “secured permission from an unspecified Russian minister” for the attack and had also “discussed” it with Syrian officials. Mr. Prigozhin would never undertake such an operation unless he felt he had clearance from the highest levels of the Kremlin.

Why risk such an attack, especially given how badly it went for Russia? Mr. Putin is constantly probing for weaknesses in adversaries, and perhaps he wanted to embarrass Mr. Trump by capturing some Americans. Perhaps he hoped to push the U.S. troops back and seize the nearby oil fields. With Mr. Trump sending no clear signals about U.S. intentions after Islamic State, and given his 2016 campaign claims that Syria is someone else’s problem, Mr. Putin might have thought that some American casualties, prisoners or a retreat would increase calls inside the U.S. to leave Syria.

The U.S. military response was impressive and laudable, but American silence about the Russian attack is puzzling. The attack shows again that Mr. Putin is looking to damage U.S. interests wherever he sees an opportunity, even at the risk of a U.S.-Russia military engagement. Maybe Mr. Trump doesn’t want to humiliate Mr. Putin, but the Russian won’t forget this defeat merely because the U.S. is quiet about it.

The danger is that he’ll interpret U.S. silence to mean that he can risk an attempt at revenge. Mr. Putin is running for re-election this spring, and while he has rigged the vote to guarantee victory, the Russian public needs to know his mercenaries suffered a humiliating defeat. If the U.S. won’t tell the truth, Mr. Putin has an easier time telling lies.

The Russian engagement also shows that the U.S. is operating a de facto safe zone for allies in eastern Syria. The Pentagon is still pursuing dispersed Islamic State fighters, but another goal is to influence the shape of post-ISIS Syria. Mr. Putin wants to push the U.S. and its allies out so its axis with Iran can dominate Syria. Look for more such confrontations to come.