WHAT IS it about poisoned tea? Russian journalist Anna Politkovskaya drank a cup of tea aboard a flight in 2004 and fell unconscious. She said she was poisoned. Later, she was assassinated by gunmen. Former KGB officer Alexander Litvinenko drank tea in a London hotel in 2006 and soon died. Alexei Navalny drank tea in an airport in Tomsk, Russia, on Aug. 20, fell violently ill and now is in a coma in a Berlin hospital that reports he, too, was poisoned. All of these tea drinkers were openly critical of Russian President Vladimir Putin and his cronies.

The events surrounding Mr. Navalny’s poisoning give rise to deep suspicion. For years, Mr. Navalny has been exposing corruption and greed among the top officials of Russia, posting videos to YouTube seen by millions of people. He has championed a method of local election organizing that eroded support for Mr. Putin’s allies. He was under near-constant surveillance by the Russian security services. On his most recent trip, the daily Moskovsky Komsomolets reported, the surveillance included “where he stayed, what he and his associates ate, whom he met, his credit card records, shopping receipts and the vehicles in which he traveled, down to a sushi order and a nighttime swim in a river.” Were they also watching when Mr. Navalny ordered tea at the Tomsk airport before a flight to Moscow?

After an emergency landing at Omsk, doctors said they couldn’t find any poison, but they strangely refused to let Mr. Navalny be transported elsewhere for treatment for nearly two days — perhaps hoping that the poison would pass from his body and be undetectable. Once he was evacuated to Berlin, doctors at the Charité hospital said, “Clinical findings indicate poisoning with a substance from the group of cholinesterase inhibitors.” This class of chemicals can be used as a nerve agent.

The Kremlin response has been chillingly indifferent. Mr. Putin’s spokesman, Dmitry Peskov, insultingly refused to say Mr. Navalny’s last name, referring to him as “the patient” and insisting any conclusion of poisoning was “hasty.”

Secretary of State Mike Pompeo reacted with utter timidity. “If the reports prove accurate” of a poisoning, he said, the United States would support the European Union’s call for an investigation. Mr. Pompeo said a probe should be transparent and hold those responsible to account. So it goes with the Trump administration, always treating Mr. Putin with kid gloves, always looking for the “if.”

The poisoning of Mr. Navalny must be thoroughly investigated, no matter where the truth leads. Since Russia is unlikely to do it honestly, an international probe is warranted. Mr. Navalny, who doctors say is not now in danger of dying, cannot become just another name on the roll call of Mr. Putin’s victims.

Who put poison in his tea — and who ordered it put there — must be found and exposed.

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