Over the last 70 years, presidential candidates have largely acted like interior designers within the existing structure of American foreign policy. Not Trump. And while it’s not clear that most Americans agree with his views, what is clear is that his candidacy comes at a time when the public is deeply conflicted about America’s outsized role in the world. A recent Pew poll found that the vast majority of Americans support U.S. membership in NATO and the United States playing a shared leadership role in the world. At the same time, however, 49 percent of Americans say U.S. involvement in the global economy is a bad thing because it lowers wages and costs jobs in the United States, compared with 44 percent who believe it’s a a good thing because it provides the country with new markets and economic growth. Fifty-seven percent want the United States to “deal with its own problems and let other countries deal with their own problems as best they can,” while 37 percent feel the “U.S. should help other countries deal with their problems.”

(The scholar Stephen Sestanovich has pointed out that the Pew results may be more indicative of partisan differences on foreign policy than of bipartisan support for the U.S. reducing its role abroad. Trump supporters are particularly likely to view U.S. involvement in the global economy as a bad thing, while Clinton supporters are particularly likely to feel the opposite.)

As William Galston of the Brookings Institution recently wrote, “[W]e now have a Trump-led nationalist party facing off against an internationalist party that will be led into battle by a former secretary of state. Internationalism represents the path of continuity, while isolationist-tinged unilateralism is a radical change.”

The last time the foreign-policy debate in a U.S. presidential election was flung this wide open was in 1952, when the Ohio senator Robert Taft tried, for the third time, to secure the Republican nomination. In The Atlantic at the time, Arthur Schlesinger, Jr. described Taft as a “New Isolationist” who reluctantly conceded that America couldn’t retreat from international affairs after the horrors of the Second World War, but disdained the new nodes of power in the postwar world, including the United Nations, NATO, and many of the structures designed to contain the Soviet Union.

“If the present policy can be briefly defined, in President Truman’s phrase, as ‘peace through collective strength against aggression,’ the New Isolationism boggles at the word ‘collective,’ and it recoils from the whole theory of building ‘situations of strength,’” Schlesinger wrote. “Its supreme emotional link with the Old Isolationism ... is its dislike of allies and its desire for unilateral action by the United States.”

Dwight Eisenhower, the celebrated World War II general and NATO commander, eventually defeated Taft in the primary, stamping out unilateralism in his party for decades to come. And he did so, in part, by making a passionate, affirmative case for internationalism and its imperfect but indispensable instruments, including the UN, NATO, and U.S. collective-security agreements (though he did want protected countries to gradually take on responsibility for their own defense rather than remain dependent on America).