Lyndon B. Johnson tried to avert a major war in Vietnam by showing restraint, in expectation of North Vietnamese reciprocation. Hanoi responded by pouring troops into South Vietnam. Richard M. Nixon revived fears of the United States with his “madman theory,” whereby he took seemingly reckless actions to convince America’s enemies that he just might be crazy enough to do it. Those fears, and the caution they instilled in the Communist powers, dissipated when the Watergate Congress kicked the legs out from under South Vietnam. The world continued to live without fear of a strong America under Jimmy Carter, whose timidity caused nations to fall to Communism and the United States Embassy in Iran to fall to anti-American extremists.

In 1980, as in 2016, Americans elected someone who made clear his intent to put fear back in the nation’s enemies. Nowadays, even liberal Democrats applaud Reagan for bringing the Soviet Union to its knees. Back in 1980, however, Reagan’s tough, nationalist stances on foreign policy aroused the same condemnation of “fearmongering” currently emanating from the world’s enlightened critics of Mr. Trump.

The trembling of the rest of the world does not ensure that American foreign policy will be successful. Like any other strategic advantage, it works only when properly exploited through sound strategic decisions. Tough talk must be used judiciously. As the Syrian red line debacle demonstrated, the White House should issue specific threats only when it is prepared to follow through on them.