Also, the business was not necessarily conducted in US jurisdiction. Facebook is a network-connected business, and the network doesn't stop at a border, as a broadcast television signal might fall off with increasing distance from the geographically fixed antenna, or as a newspaper or magazine that is delivered to a mailing address might never again migrate further than the distance from the coffee table to the trash can.
If a Russian wants to tell someone in Germany that Hillary Clinton is just the worst, I don't think the US has any reason to expect it can stand between them and say they can't do that, just because she happens to be running a political campaign--especially since political campaigns in the US are interminably long and tedious, such that a public figure might be expected to be continuously connected to one political campaign or another for decades.
I think probably the best that could happen there is a disclosure rule, such that anyone that transmits such messages to a US recipient has to be able to identify the person or organization that created it, or to warn the recipient that the sender could not be identified.