Russiagate is a hoax invented by the American Deep State.
Recurring pro-Kremlin disinformation combining claims on the lack of Russian interference in the 2016 US presidential election, the Mueller report, and a conspiracy theory about the deep state, in the US or or elsewhere.
Robert Mueller's investigation concluded that Russia did interfere in the 2016 election. Robert Mueller’s report maintains that “the investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities”. Nevertheless, it states that Russian interference activities did take place. See here for full Mueller report.
As concluded earlier by the US intelligence community and by Mueller’s own inquiry “the investigation established that the Russian government perceived it would benefit from a Trump presidency and worked to secure that outcome, and that the Campaign expected it would benefit electorally from information stolen and released through Russian efforts”.
For further debunking, see here.
For other cases about Russian interference in the US elections 2016, see here.