Earlier quoted context omitted.
Freedom of speech is not just to protect the speaker, it's to protect the rights of the citizens to hear it. Foreign propaganda is explicitly legal and protected in the United States. I'm sorry that you think it should not be, but it is, and it always has been throughout the entire history of the country. How exactly do you intend to distinguish the types of speech that the government is allowed to ban? Any foreign o…
The parent comment referenced misinformation campaigns. False statements are one of several categories of speech that are not protected.
The standard in the United States is that the information published is both knowingly false and published with actual malice. And for matters of public concern, there is a further requirement that the information be provably false. Separately, the charges cannot be ridiculous, as demonstrated in Hustler v. Falwell, where it was held that even though Hustler published a story that Jerry Falwell had incestuous sex with his mother in an outhouse, and even though that story was false, known by the publisher to be false, and published with actual malice, it still did not meet the standard.
Misinformation campaigns are absolutely allowed in the United States. This is a current problem with Fake News. Fake news is protected by the First Amendment, no matter who writes it. And indeed, much of it is written by foreign agents, specifically with the intent of influencing US elections.