The target was Aleksandr Poteyev, a former Russian intelligence officer who disclosed information that led to a yearslong F.B.I. investigation that in 2010 ensnared 11 spies living under deep cover in suburbs and cities along the East Coast. In keeping with an Obama administration effort to reset relations, a deal was reached that sought to ease tensions: Ten of the 11 spies were arrested and expelled to Russia. According to Mr. Walton’s book, a Kremlin official asserted that a hit man, or a Mercader, would almost certainly hunt down Mr. Poteyev. Based on interviews with two American intelligence officials, Mr. Walton concluded the operation was the beginning of “a modern-day Mercader” sent to assassinate Mr. Poteyev.

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Persons: Aleksandr Poteyev, Obama, Sergei V, Mr, Poteyev, Brown, Calder Walton, Walton’s, Ramón, Joseph Stalin’s, Leon Trotsky’s, Walton, Mercader ”, Grigory Mairanovsky Organizations: Intelligence, Harvard, The New York Times, Kremlin Locations: Russian, East Coast, Russia, Moscow, Britain, Mexico City, S.V.R