These efforts shifted over time, peaking at key political moments, such as presidential debates or party conventions, the report found.
The data sets used by the researchers were provided by Facebook, Twitter and Google and covered several years up to mid-2017, when the social media companies cracked down on the known Russian accounts. The report, which also analysed data separately provided to House intelligence committee members, contains no information on more recent political moments, such as November's Midterm election.
"What is clear is that all of the messaging clearly sought to benefit the Republican Party — and specifically Donald Trump," the report says.
"Trump is mentioned most in campaigns targeting conservatives and right-wing voters, where the messaging encouraged these groups to support his campaign. The main groups that could challenge Trump were then provided messaging that sought to confuse, distract and ultimately discourage members from voting."
Representatives for Burr and Warner declined to comment.
The new report offers the latest evidence that Russian agents sought to help Trump win the White House.
Democrats and Republicans on the panel previously studied the US intelligence community's 2017 finding that Moscow aimed to assist Trump, and in July, they said investigators had come to the correct conclusion. Despite their work, some Republicans on Capitol Hill continue to doubt the nature of Russia's meddling in the last presidential election.
The Russians aimed particular energy at activating conservatives on issues such as gun rights and immigration, while sapping the political clout of left-leaning African-American voters by undermining their faith in elections and spreading misleading information about how to vote.
Many other groups — Latinos, Muslims, Christians, gay men and women, liberals, southerners, veterans — got at least some attention from Russians operating thousands of social media accounts.
The report also offered some of the first detailed analyses of the role played by YouTube, which belongs to Google, and Instagram in the Russian campaign, as well as anecdotes on how Russians used other social media platforms — Google+, Tumblr and Pinterest — that have gotten relatively little scrutiny. The Russian effort also used email accounts from Yahoo, Microsoft's Hotmail service and Google's Gmail.
The authors, while reliant on data provided by technology companies, also highlighted their "belated and uncoordinated response" to the disinformation campaign and, once it was discovered, for not sharing more with investigators. The authors urged the companies in the future to provide data in "meaningful and constructive" ways.
Facebook, for example, provided the Senate with copies of posts from 81 Facebook "Pages" and information on 76 accounts used to purchase ads but did not share the posts from other user accounts run by the IRA, the report says. Twitter, meanwhile, has made it challenging for outside researchers to collect and analyse data on its platform through its public feed, the researchers said.
Google submitted information in an especially difficult way for the researchers to handle, providing content such as YouTube videos but not the related data that would have allowed a full analysis. The YouTube information was so hard for the researchers to study, they wrote, they instead tracked the links to its videos from other sites in hopes of better understanding YouTube's role in the Russian effort.
Facebook, Google and Twitter didn't immediately respond to requests for comment.
They first disclosed last year that they had identified Russian meddling on their sites.
Critics previously said it took too long to come to an understanding of the disinformation campaign, and that Russian strategies have likely shifted since then. The companies have awakened to the threat — Facebook in particular created a "war room" to combat interference around elections — but none have revealed interference around the Midterm elections last month on the scale of what happened in 2016.
The report expressed concern about the overall threat social media poses to political discourse within nations and between them, warning that companies once viewed as tools for liberation in the Arab world and elsewhere are now threats to democracy.
"Social media have gone from being the natural infrastructure for sharing collective grievances and coordinating civic engagement to being a computational tool for social control, manipulated by canny political consultants and available to politicians in democracies and dictatorships alike."
Researchers also noted that the data includes evidence of sloppiness by the Russians that could have led to earlier detection, including the use of Russia's currency, the ruble, to buy ads and Russian phone numbers for contact information. The operatives also left behind technical signatures in computerised logs, such as Internet addresses in St Petersburg, where the IRA was based.
Many of the findings track in general terms work by other researchers and testimony previously provided by the companies to lawmakers investigating the Russian effort. But the fuller data available to the researchers offered new insights on many aspects of the Russian campaign.
The report traces the origins of Russian online influence operations to Russian domestic politics in 2009 and says that ambitions shifted to include US politics as early as 2013 over Twitter.
Of the tweets the company provided to the Senate, 57 per cent are in Russian, with 36 per cent in English and smaller amounts in other languages.
The efforts to manipulate Americans grew sharply in 2014 and every year after, as teams of operatives spread their work across more platforms and accounts, in order to target larger swaths of US voters by geography, political interests, race, religion and other factors. The Russians started with accounts on Twitter, then added YouTube and Instagram before finally bringing Facebook into the mix, the report said.
Facebook was particularly effective at targeting conservatives and African-Americans, the report found.
More than 99 per cent of all engagement — meaning likes, shares and other reactions — came from 20 "Pages" controlled by the IRA, including "Being Patriotic," "Heart of Texas," "Blacktivist" and "Army of Jesus."
Together the 20 most popular pages generated 39 million likes, 31 million shares, 5.4 million reactions and 3.4 million comments.
Company officials told Congress that the Russian campaign reached 126 million people on Facebook and 20 million more on Instagram.
The Russians operated 133 accounts on Instagram, the photo-sharing subsidiary of Facebook, that focused mainly on race, ethnicity or other forms of personal identity. The most successful Instagram posts targeted African American cultural issues and black pride and were not explicitly political.
While the overall intensity of posting across platforms grew year by year — with a particular spike during the six months after Election Day — this growth was particularly pronounced on Instagram, which went from roughly 2600 posts a month in 2016 to nearly 6000 in 2017, when the accounts were shut down. Across all three years covered by the report, Russian Instagram posts generated 185 million likes and four million user comments.
