Today it means: Suggesting the ability of a politician with an unassailable reputation among his or her supporters for representing and defending their values to take actions that would draw their criticism and even opposition if taken by someone without those credentials. Full definition →
A reference to U.S. President Richard Nixon's 1972 establishment of direct diplomatic relations with, and personal visit to, the People's Republic of China. Nixon's unyielding opposition to Communism had been well-known.
Etymology from Wiktionary, CC BY-SA 4.0.