I don't think the argument was that Clinton voters switched to Trump. More that Clinton voters were persuaded to stay home. Which is a perfectly valid campaign strategy -- e.g. why campaign funds are so vital to a successful campaign. But political advertising is required to have disclosures. That foreign actors were allowed to push propaganda with the aim of influencing the election with the unknowing assistance of Facebook can still be considered a problem, no matter which candidate it was for.
Frankly speaking, if someone should took the blame for Clinton voters staying home, it's traditional media. They were constantly talking how her victory is predicated, how she is supposed "to take Ohio, to take Florida, to take Wisconsin", NYT and HuffPost showing election calculators with "95% probability of Hillary winning" (Nate Silver was the only one who said that Trump has 30% chance, and he was laughed out of the room for that!).
Is it really a mystery that democratic voter turnout was low? Why they should be bothered if the victory in their pocket? And Trump voters were energized beyond belief by the exactly same message from traditional media.
Of course traditional media is primarily to blame for this outcome, but legislators have no business addressing the 1st Amendment-protected activities of the New York Times et al.
Lawmakers have a duty to mitigate foreign interference in U.S. elections. Foreign campaign political campaigns, through traditional and social media, need to be monitored and regulated. The regulation is there. The enforcement is still catching up.
