Most Americans know the song “MTA,” popularized by the Kingston Trio in 1959. It’s the one about a “man named Charlie” doomed to “ride forever ’neath the streets of Boston . . . the man who never returned.” What’s forgotten, however, is that the song was originally made for a left-wing political campaign. In 1949, the Boston People’s Artists wrote “MTA” for a left-wing candidate. The song became a hit — the man behind it disappeared.