It's been reported that 13 Russian Federation citizens have been indicted in the US for waging a misinformation campaign during the last Presidential election cycle in the hopes of sowing discontent. They were indicted because (presumably) foreign nationals have no business making their opinion have undue influence on US elections.
It is known (or at least it is alleged) that the trolls were paid. Had they been US citizens, would that have been legal? They were not directly lobbying any government officials. So they didn't have to register as lobbyists. They did not work (at least not directly) for the Russian government.
The allegation is that they worked for foreign private companies. If these were US citizens, they would have been in the same situation as US citizens who work for any other private business in Russia who decide to espouse any kind of political views on their social media accounts. Which means they would not have had to register as foreign agents (because they would not work for a government).
They did not advocate for war or (at least according to the reports) for violence. So they did not incite rebellion or violence.
This may seem like a rhetorical question, but I genuinely can't tell anymore what's legal in this respect. Is it illegal for US citizens to accept payments (from foreign private concerns) for shilling political opinions they don't personally hold?
I guess this can count as political advertising by foreign private interests, but is it illegal to accept money from foreign entities to place political ads? Clearly, it's illegal for foreigners to buy political ads, but is it illegal to sell ad space for political ads to foreigners?
The 13 Russians who were indicted were not charged with accepting payments for illegal campaign ads (which is not to say that they didn't do it). But would that be something that US citizens have to be wary of?
By the way, I am obviously asking this in the context of the 1st Amendment.