The intelligence agencies’ report on the Russian intervention in the American presidential election portrays it as just one piece of an old-fashioned Soviet-style propaganda campaign. But it was a campaign made enormously more powerful by the tools of the cyberage: private emails pilfered by hackers, an internet that reaches into most American homes, social media to promote its revelations and smear enemies.

What most Americans may have seen as a one-time effort — brazen meddling by Russia in the very core of American democracy — was, the report says, only part of a long-running information war that involves not just shadowy hackers and pop-up websites, but also more conventional news outlets, including the thriving Russian television network RT. The election intervention to damage Hillary Clinton and lift Donald J. Trump was the latest fusillade in a campaign that has gone on under the radar for years.

For the three agencies that produced the report — the C.I.A., the F.B.I. and the National Security Agency — this is a heart-stopping moment: They have just told their new boss that he was elected with the vigorous, multifaceted help of an adversary, the thuggish autocrat who rules Russia.

“Putin and the Russian government aspired to help President-elect Trump’s election chances when possible by discrediting Secretary Clinton and publicly contrasting her unfavorably to him,” the report says, in unusually blunt and sweeping language.