a fellow traveler

Someone who identifies with or is sympathetic to the aims or ideology of a political movement or organization, but is not a formal or full member of it. Used especially in the 1950s in reference to those suspected of being communist sympathizers. In my grandfather's day, if someone accused you of being a fellow traveler, it was often to derail your career completely. Despite having a mark against him as a "fellow traveler," he still managed to remain at the Hollywood elite.

A fellow traveller is someone who supports the aims of an organization but is not a member of it. Note: `Traveller' is spelled `traveler' in American English. Although something of a critical fellow traveller, Sampson was very interested in the party.

Someone sympathetic to the beliefs and activities of an organization but not a member of that group. The phrase originally applied to people in the early days of the Soviet Union who supported the Russian revolution and the Communist Party but were not members. Communism was popular among many American intellectuals during the 1930s and '40s, but following World War II, this country's attitude toward the Soviets changed in light of Stalin's purges and revelations of espionage. Accusations that Soviet sympathizers had infiltrated our government and military led to congressional investigations, and the phrase “fellow traveler” was used to label those accused of “un-American” activities or even just “Communist dupes.” Many such people found themselves blacklisted or otherwise persecuted. A rarely used vestige of the phrase now applies to anyone who agrees with any viewpoint or faction but does not publicly work for it. The Soviet Union named its early space satellites “Sputnik,” the Russian word for “fellow traveler.”