In fact, I think the biggest threat to the US is the suspension of the first amendment because of the age old boogeyman of national security. Propaganda has always existed. The way to respond to bad speech is more speech. Banning it makes it forbidden and thus captivating, don't you know about the Streisand Effect?
If the transmission of media is a threat to national sovereignty, if the fate of the country can be undermined with memes, then we have already lost. The US should disconnect itself from the global internet.