Story highlights One theory among Democrats: Russia was behind spikes in anti-Clinton fake news

Trump campaign staff said Facebook testimony could clear their names

Congressional investigators likely to face a tough battle trying to get answers

(CNN) Top Democrats on the House and Senate Russia investigations and a top digital staffer from the campaign of President Donald Trump split sharply on whether the campaign colluded with Russia, but many agree that Facebook holds the answers investigators are looking for and they want the social media giant to give up the goods.

Virginia Sen. Mark Warner, the top Democrat on the Senate intelligence committee, met with Facebook officials in California more than a month ago as part of his committee's investigation into potential collusion or election interference, and he's convinced the company can explain whether anyone from the Trump campaign helped Russians boost fake news articles targeting Democratic presidential nominee Hillary Clinton. Warner is testing the theory popular among Democratic operatives that Russia was behind spikes in fake news that were anti-Clinton and that Russia had help targeting those articles from US political operatives.

"If the Russians know, how are the Russians smart enough to target in areas where the Democrats weren't knowledgeable enough? I don't feel like I have run that to ground yet," Warner told CNN.

"There are two questions. One is: Was there coordination or collusion between the campaigns and these technology tools, which overwhelmed the search engine tools so that certain stories popped up at the top of your newsfeed. The second is, on a broader basis going forward: How do we prevent this from happening again?" Warner said.

Likewise, House investigators plan to interview former Trump campaign digital director Brad Parscale as part of their probe. A Democratic committee source said they want to know whether Parscale or anyone else from the campaign helped guide Russian targeting of fake news stories.

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