U.S. intelligence sources who are close to Russian President Vladimir Putin and the Kremlin have reportedly “gone silent” in the run-up to the 2018 midterm elections, The New York Times reports. The informants previously provided the U.S. with “critical details” about Russian efforts to meddle in the 2016 election. Now, they have left the Central Intelligence Agency and others “in the dark” about Putin’s intentions ahead of the November elections. Sources told the newspaper that they don’t believe informants have been killed, but think they may gave gone underground amid more “aggressive counterintelligence” efforts in Russia—including the use of the nerve agent Novichok against Sergei Skripal, a former spy. This comes as The Daily Beast reported that Russians attempted to hack into Sen. Claire McCaskill’s email and as Facebook detected more foreign actors participating in coordinated political activity on the social-media platform.