Merriam-Webster defines a “fifth column” in its original, literal sense: “a group of secret sympathizers or supporters of an enemy that engage in espionage or sabotage within defense lines or national borders.” That is a high bar (i.e., hidden agents under foreign direction with actions timed to a military objective), and almost nothing discussed in American politics today clears it.
The term has widened in recent years. Political scientists now treat fifth-column politics as rhetoric, policy, or mobilization against domestic “enemies within.” Scott Radnitz of the University of Washington splits it into two types: subversive claims aimed at vulnerable minorities or immigrants and collusive claims aimed at elites said to serve a foreign power. Neither needs a hidden army or single chain of command. Both describe a domestic network—whether organized or not—whose activities, funding, or ideology line up with a foreign adversary, or that treats the U.S. constitutional order as illegitimate and works to replace it from the inside.
