Public discussion about the character and fitness for office of presidential candidates is at the core of the First Amendment's command that "Congress shall make no law . . . abridging the Freedom of Speech." Yet Congress, in its zeal to impose onerous campaign-finance restrictions, has made political speech a felony for one class of speakers. Corporations and unions can face up to five years in prison for broadcasting candidate-related advocacy during federal elections.

Is outlawing political speech based on the identity...