I'm not so sure I agree with making social media networks the problem when it comes to such shannanigans as apparently played by the Russians. It's more of a manipulation of advertising services than "Facebook" when it comes to the Russians buying ads. It's more of a manipulation of the population than it is of Twitter's "user base".
Hey CBS, how many times were you played by companies manipulating people to spend money on cars and toilet paper?
Before the Internet people bought ads on TV and radio. And before Facebook and Twitter people bought display ads on the raw WWW, if they did not outright build websites themselves (for younger visitors, a "website" is similar to a "Facebook Page").
I am not sure why the drum beat is to corner Twitter and Facebook into "doing something" to somehow screen the communication of digital humanity taking place in their 'hoods unless it is purposeful pressure to apply yet a little more control and containment of free interaction in general.
The mainstream media, I've theorized for some time, is poised to begin taking pot shots at social media giants whenever it can with the hopes of bogging down their economics and reputation. Making them the focal point in the Russian propaganda campaign strikes me as just one example.