An expression used by Soviet intelligence to describe non-communist leftists who could be manipulated into supporting Soviet communism by spreading planted lies, the term "useful idiot" now more broadly refers to anyone who unwittingly serves as a disease vector in the viral spread of disinformation. It's my new favorite term.
Check your sources. Doubt extremist memes, even if you want them to be true. Don't be a useful idiot.
This 3-part opinion/editorial video series, published by the New York Times, gives a great background for the term. It starts with a fascinating history of Soviet disinformation during the Cold War. (Did you know the KGB invented the conspiracy theory that the U.S. government secretly created the AIDS virus as a biological weapon? Despite Russia's later confessing to having invented the story as part of Operation INFEKTION, millions of Americans -- including Kanye West -- still believe it.)
The video then goes on to discuss more recent Russian disinformation campaigns, and the torrent of disinformation coming from the Trump White House. It's about 45 minutes in all, but well worth the time, in spite of its sometimes overly-dramatic production.