A new report prepared for the Senate concludes that Russia used every major social network to support Donald Trump during the 2016 election and continued to support him after he was elected president.

“ ‘What is clear is that all of the messaging clearly sought to benefit the Republican Party — and specifically Donald Trump.’ ”

The Washington Post reported Sunday that it had obtained a draft copy of the report, which studied millions of social-media posts on Facebook FB, +0.29% , Twitter TWTR, -4.56% , Alphabet Inc.’s Google GOOGL, +1.11% GOOG, +1.16% and other platforms, for the Senate Intelligence Committee. The report is expected to be made public this week.

The tech companies provided data for several years of posts, through mid-2017, the Post reported. The report by Oxford University’s Computational Propaganda Project and network analysis company Graphika found that a Russian disinformation campaign using thousands of accounts targeted American voters over the course of years, with evolving messages that peaked around key moments, such as the party conventions and presidential debates.

“Trump is mentioned most in campaigns targeting conservatives and right-wing voters, where the messaging encouraged these groups to support his campaign,” the report said, according to the Post. “The main groups that could challenge Trump were then provided messaging that sought to confuse, distract and ultimately discourage members from voting.”

The report found that Russia used the issues of gun control and immigration to energize conservatives, while discouraging African-Americans — traditional Democratic voters — from voting by undermining their faith in the electoral process and spreading lies about how to vote.

While the main social networks used for disinformation were Facebook, Twitter and Google’s YouTube, the report found Russia also used Facebook-owned Instagram, Google+, Pinterest and Verizon Communications Inc.’s VZ, +0.57% Tumblr.

The report warned that in the U.S. and other parts of the world, social networks have moved away from their original purpose of sharing and community toward “being a computational tool for social control, manipulated by canny political consultants and available to politicians in democracies and dictatorships alike.”