"We see no reason to dispute the conclusions," Senate Intelligence Committee Chairman Richard Burr stated.
According to the Department of Homeland Security, 21 states were targeted, but a small number of them were "successfully penetrated."
Investigators have obtained 15 search or seizure warrants.
Trump Jr. received an email offering a decryption key and website address for hacked WikiLeaks documents.
Accusations between Democrats and Republicans come a week after special counsel Robert Mueller moved forward with charges against Trump campaign members.
Tweets from Russian accounts pushed praise for Trump over criticism by close to a 10-to-1 margin
Republican lawmaker says Mueller "must step down immediately” because of ties to the Obama administration.
Among those who felt President Donald Trump likely committed a crime, 19 percent believed there was solid evidence
The Senate Judiciary Committee launched a probe last week and the House Intelligence Committee may also open an investigation
Senator says Obama administration “should have known, you would think, about what was going on "
Informant could not disclose information he gathered on Russian racketeering because he signed a nondisclosure agreement with the FBI
Senators are expected to grill Attorney General Jeff Sessions today.
Republicans say there are "numerous reports emerging almost every day" of Robert Mueller and his team engaging in conflicts of interest
Roger Stone, a longtime Donald Trump confidant, will testify Tuesday about alleged Russian meddling in U.S. politics, but only behind closed doors.