“Madman Theory.” That’s when adversaries tread carefully because they suspect the U.S. president of being unpredictable, occasionally reckless and potentially crazy dangerous. Henry Kissinger, with Nixon’s collaboration, tried more than once to exploit this perception to pressure adversaries."

Reagan had a similar effect every now and then.  "My fellow Americans, I'm pleased to tell you today that I've signed legislation that will outlaw Russia forever. We begin bombing in five minutes."