Congress passed the act in 1938 which was intended to force agents of enemy governments such as Nazi Germany or the Soviet Union to self-identify so the public could evaluate their speech or propaganda in light of their stated loyalties. Between 1966 and 2015, the DOJ brought a total of seven cases, only one of which resulted in a conviction. Beginning in 2016, however, FARA cases became all the rage. The Justice Department created a new unit dedicated to sniffing out potential violators. On its surface, the statute has a politically neutral objective of informing the public of foreign influence. In practice, however, the law has become the go-to tool for partisan federal prosecutors. FARA prosecutions have tended to focus on Republicans (see Flynn, Guiliani, Manafort, etc.) even when Democrats commit the mirror image of the same violations (see Tony Podesta, Joe Biden, John Kerry, etc.)
As mentioned, one obvious example was the blatantly political selection of Paul Manafort as a FARA defendant, while politically connected Tony Podesta received an immunity deal for essentially the same behavior involving the same foreign clients.
Fusion GPS, which famously underwrote the Russia collusion hoax dossier, has piled up multiple FARA complaints (including unregistered work for Russia) that the Justice Department continues to ignore.
FARA is vague and subject to unbridled prosecutorial discretion. To demonstrate how vague, travel agents now register as “foreign agents” under the theory that marketing a tourist trip is a legally reportable act. It’s a perfect weapon to invoke secret surveillance pursuant to FISA and can be used against anyone with an international clientele. Nobody really knows what’s illegal until the Justice Department targets you. Then they can make it up and tamper with testimony to create their own crime when one doesn’t exist.