Putin is an expert in poisoning dissidents. Trump shouldn't just let this happen.

Curiously, however, Putin has suffered little from the most sinister of his international operations: the murders of fleeing spies and other exiled opponents. According to some figures, more than a dozen people have been murdered by Kremlin agents since 2004, while a number of others have barely survived the attacks.

Two of these actual or attempted murders, of former spies Alexander Litvinenko and Sergei Skripal, took place in Britain, where they provoked controversy and the expulsion of dozens of Russian diplomats from London and 39; other western capitals. But a more typical case is the murder last August in Berlin of a Chechen activist in exile. Although authorities have captured the hitman and identified him as a Russian agent, the only consequence imposed by the German government so far has been the expulsion of two diplomats.

Even a few other successes in Britain, and perhaps one or two in the United States, did not elicit much reaction. This is partly because of their profession: if certain assassinations were committed by bullet (as in Berlin) or even by car bomb, the majority relied on the use of exotic poisons, a Russian technique that dates back to the Cold War. The KGB attempted to kill the writer Aleksandr Solzhenitsyn with ricin; more recently, his successor, the FSB, and the military GRU were captured using dioxin, gelsemium, cadmium, polonium and the nerve agents sarin and Novichok.

In some cases, the nature of the poison has never been determined, which has allowed Moscow to question the premature death of a dissident. In this regard, no case is more intriguing or, perhaps, more urgent than that of activist Vladimir Kara-Murza, former senior official of the killed opposition leader Boris Nemtsov. Kara-Murza, who publishes articles on The Post, is a permanent American resident who divides his time between Moscow and the outskirts of Washington, Virginia, where his family lives.

He was poisoned twice in Moscow, in May 2015 and in February 2017. In both cases, he suffered multiple organ failures and barely survived. Each time, Russian doctors said he was suffering from acute poisoning by an unidentified substance. However, in none of the cases, this poison identified, and there were no consequences for those who committed the attacks.

It was not for lack of trying. After the 2017 poisoning, Evgenia, Kara-Murzas' wife, carried a hand blood sample in Washington, where she was met at the airport by FBI agents. The FBI took custody of the blood sample and performed tests. According to Vladimir Kara-Murza, an FBI agent met him in late 2017 and reported that signs of poisoning had been found in his blood and that the full results would soon be provided.

Then came a curious delay: a few weeks later, says Kara-Murza, the FBI agent called him to tell him that there were inconsistencies between the different tests and that the results would be delayed. So, silence. The agency did not respond to requests for further results from Kara-Murzas, or to letters from several members of Congress requesting them. In July 2018, Kara-Murza filed appeals under the Freedom of Information Act and the Privacy Act. Again, no answer.

The dissident wonders if the offices' failure to communicate has anything to do with a meeting between senior Russian and American intelligence officials in Washington in January 2018. Kara-Murza said the FBI agent told him had said that a report on his poisoning would be given to visitors. FSB and GRU directors.

Or maybe the FBI's silence is the result of mundane bureaucratic delays. Either way, US officials are sitting on test results that can show how the Putin regime twice attempted to kill a peaceful opponent whose close ties to the United States, and the columns of the Post, recall Jamal Khashoggi, the murdered Saudi journalist.

Last week, lawyers volunteering for Kara-Murza filed a complaint in a US district court in Washington requesting the publication of test results. The activist himself was back in Moscow to commemorate the fifth anniversary of the murder of Nemtsov. The test results, he emailed me, could be a small measure of protection from repeated attacks on my life.

True, the Trump administration isn't much to defend dissidents or hold Putin accountable. But that doesn't seem to ask much.