The evolution of the Republican Party in the past several months has been breathtaking to witness. The party of Reagan is now deeply suspicious of free trade and security alliances while growing ever more fond of Russian autocrat Vladimir Putin. Policy positions, especially in trade and foreign policy, have flipped with such extraordinary speed that it seems like there must be some core instability in the party, a will to power that has shattered any foundational principles.

That may be true. But the party's rapid abandonment of long-held principles has been possible in large part because it draws on the right's deeper history, a history that reaches back before the Cold War to a nascent conservative movement. That movement grew not out of McCarthyism but an inward-looking nationalism, one that has re-emerged with Donald Trump.

The story of modern American conservatism cannot be understood without first understanding the America First Committee, the short-lived anti-interventionist movement founded in 1940. Its members ran the ideological spectrum – socialists, progressives, conservatives, fascists – but the AFC drew most of its membership from around Chicago, where conservative nationalism flourished in the 1940s and 1950s.

The AFC dissolved after the attack on Pearl Harbor, but a few years later a number of its members reconvened in Chicago to help launch "Human Events," which would become an influential conservative newsweekly. "Human Events" was sharply out of touch with the prevailing foreign policy preferences of the mid-1940s, especially when the editors made the case for an easy peace with Germany. Indeed, the editors fielded numerous complaints from readers who felt "Human Events" was too sympathetic to Germany, leading them to moderate their coverage.

Conservative nationalists in the 1940s and 1950s fretted about the U.S. becoming too involved in the postwar world, offering an alternative to Henry Luce's call for an American Century, one with the U.S. as the world leader. They worried that the U.S. would sacrifice its sovereignty if it became too entangled in international governance, that it would lose its ability to act unilaterally.

The rapid escalation of the Cold War shattered conservative nationalism. Its adherents either became committed Cold Warriors or were pushed to the fringes of the conservative movement. Multilateralism still had its critics – the John Birch Society constantly called on the U.S. to get out of the U.N. – but that protectionist, predominantly noninterventionist nationalism faded. The Cold War fashioned a conservatism devoted to militant anti-communism and rigorous free-trade rhetoric. That was Reagan's conservatism.

No sooner had the Cold War ended than that old conservative nationalism, restyled as paleoconservatism, re-emerged. Pat Buchanan bore their standard, reviving protectionism and a stay-at-home nationalism within the GOP. He even sought to found a new America First Committee, believing America needed a return to its pre-World War II approach to world affairs.

Buchanan never won the Republican nomination, but he did remain an important force in the party during the 1990s, a decade when the central organizing principle of American politics – the Cold War – had disappeared, and anything seemed possible. Buchanan was also a leading figure in the culture wars, arguing against secular, feminism and pluralism. He has long viewed America as a white Christian nation under threat from minorities and immigrants. Those views, however, were not out of step with the GOP in the way his views on foreign policy and trade were.

For Republicans, the start of the War on Terror largely ended the post-Cold War foreign policy debate. Buchanan was driven out of mainstream Republican and conservative circles for his criticism of the decision to invade Iraq.

But Buchanan's exile was short-lived. The invasion of Iraq quickly turned sour, the economy collapsed and now the GOP and the Buchananites have aligned in the policies of Donald Trump. It turns out that, absent the Cold War, Republicans had little lasting commitment to ideas like free trade and internationalism. With the Cold War out of the way and the spectacular failures of neoconservative foreign policy on display in Iraq, the right has, with stunning speed, returned to its roots.

Originally published in U.S. News & World Report.