"In May 2016, a Russian military intelligence officer bragged to a colleague that his organization, known as the GRU, was getting ready to pay Clinton back for what President Vladimir Putin believed was an influence operation she had run against him five years earlier as Secretary of State. The GRU, he said, was going to cause chaos in the upcoming U.S. election. What the officer didn't know, senior intelligence officials tell TIME, was that U.S. spies were listening. They wrote up the conversation and sent it back to analysts at headquarters, who turned it from raw intelligence into an official report and circulated it. But if the officer's boast seems like a red flag now, at the time U.S. officials didn't know what to make of it. "We didn't really understand the context of it until much later," says the senior intelligence official. Investigators now realize that the officer's boast was the first indication U.S. spies had from their sources that Russia wasn't just hacking email accounts to collect intelligence but was also considering interfering in the vote. Like much of America, many in the U.S. government hadn't imagined the kind of influence operation that Russia was preparing to unleash on the 2016 election. Fewer still realized it had been five years in the making."