THE REPORTED plot by Russia’s military intelligence service to pay a bounty to the Taliban in Afghanistan for killing U.S. and coalition forces, if confirmed, will mark another escalation of Russia’s conflict with the West, a turn in the shadow wars that would seem to cry out for a forceful response. President Trump’s reaction in recent days — that he wasn’t told, that it is a hoax — has been utterly inadequate.

The New York Times and The Post reported that U.S. intelligence agencies concluded months ago that a Russian military intelligence unit offered money for killing Americans last year, and one piece of evidence was the discovery in a raid on a Taliban outpost of a large amount of U.S. cash. The reports added that interrogations have made the intelligence community confident in its assessment that the Russians had offered and paid bounties in 2019; the assessment resulted in a high-level interagency meeting at the White House in late March to consider possible responses. The bounties are believed to have caused the death of at least one soldier. The Times reported that Mr. Trump was briefed on the intelligence.

Why Russia did this can only be guessed at, but it clearly fits with President Vladimir Putin’s pursuit of asymmetric warfare against the West, from cyberattacks and interfering in the 2016 U.S. election to an attempted poisoning of a former spy in Britain. Mr. Putin, a former Soviet KGB officer, has encouraged his intelligence services to be more aggressive overseas.

A proper U.S. response would begin with loud and open protest to Mr. Putin. It would expose enough of the intelligence to make it credible, and then the United States would work with NATO allies on sanctions and other measures. It is definitely not the time to invite Russia to join the Group of Seven leaders at their next meeting, as Mr. Trump suggested this month.

Mr. Trump’s response has been stupefying. “Nobody briefed or told me,” Mr. Trump insisted on Twitter. How could the president not be informed about such reports? Was it written in his daily brief and he didn’t read it? It’s hard to say which would be more damning: that he was informed and is denying that now, perhaps because he took no action in response to the intelligence; or that nobody in his administration bothered to clue him in on a highly consequential development. If the latter, shouldn’t Mr. Trump’s reaction now be: Why not, and what’s going on?

Rather than address the highly disturbing news itself, Mr. Trump offered more distractions and denials, claiming the intelligence agencies “did not find this info credible, and therefore did not report it to me.” He added, “Possibly another fabricated Russia Hoax . . . wanting to make Republicans look bad!!”

The intelligence reports, if true, demand a serious response. With Mr. Trump once again immobilized in the face of Russian provocation, Congress will have to step up. It could start by approving the long-pending Deter Act, aimed at discouraging Russian interference in this year’s election, and investigating the latest intelligence and U.S. nonresponse.

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