Trust, but verify

Trust, but verify is a translation of a Russian proverb, which became well known when used by President Ronald Reagan in the context of nuclear disarmament.

Suzanne Massie, a writer in Russia, met with President Ronald Reagan many times between 1984 and 1987. She taught him the Russian proverb, "Доверяй, но проверяй" {Doveryai, no proveryai} (trust, but verify) advising him that "The Russians like to talk in proverbs. It would be nice of you to know a few. You are an actor – you can learn them very quickly." The proverb was adopted as a signature phrase by Reagan, who subsequently used it frequently when discussing U.S. relations with the Soviet Union. Using proverbs that the Russians could relate to may have helped relations between the two leaders.

After Reagan used the phrase to emphasize "the extensive verification procedures that would enable both sides to monitor compliance with the treaty", at the signing of the INF Treaty, on 8 December 1987, his counterpart General Secretary Mikhail Gorbachev responded: "You repeat that at every meeting," to which Reagan answered "I like it." While Reagan quoted Russian proverbs, Mr. Gorbachev quoted Ralph Waldo Emerson, who had been popular in the USSR when Gorbachev was in college, saying that "The reward of a thing well done is to have done it."

Following the 2013 Ghouta attacks, Secretary of State John Kerry told a news conference in Geneva on September 14, 2013 that the United States and Russia had agreed on a framework to dispose of Syria's chemical weapons. He said "President Reagan's old adage about 'trust but verify' ... is in need of an update. And we have committed here to a standard that says 'verify and verify'."

...
Wikipedia