Measuring Russian meddling in 'likes' and 're-tweets'

It's now common knowledge that Russia tried to influence last year's election in favor of Donald Trump. What was the role of social media? Facebook's Mark Zuckerberg said that question was "crazy" — until he was warned personally by Barack Obama.

Now Facebook and Twitter are under scrutiny by Congress and Special Prosecutor Robert Mueller. Can Tech be trusted to police its advertisers? What about campaign finance rules like those for print and broadcast? We hear about digital communications, politics and freedom of speech.