No one riding the Trump “platform” has been elected president. But that does not mean his protectionist isolationist vision isn’t appealing or deeply rooted in American history.

Donald Trump’s varied proposals for border control, economic progress, and national security seem scattered. But his inward-oriented economic and foreign policy outlook helps unify them. At the highest national level such a position has never been a path to the White House, but it has been a path to political prominence. It also has been far more popular historically than many today appreciate.

At its most basic level, isolationism has been a foreign policy premised on maintaining national autonomy—interests, rights, and self–sufficiency—generally without alliances and without binding treaties with other nations.

There have been two main strains of isolationist thought in U.S. foreign policy: political and protectionist. Both have been heavily stigmatized and often slung as an epithet against opponents of particular foreign policies. Almost no one in the American tradition has ever advocated a fully walled-and-bounded United States. Instead, political isolationist arguments now as in the past have internationalist components but rely on skepticism to inform them. Isolationists and non-interventionists have tended to embrace a few core beliefs:

● they have rejected or been very restrained about collective security and international organizations (Trump on NATO, UN);

● they frequently opposed compromises inherent in multilateral binding diplomacy (Trump on Iran nuclear accord, TPP);

● they often rejected interventions or were reticent about “globalism” (Trump on Iraq, Afghanistan, and elsewhere);

● they almost always aimed to restrict immigration (often tainted by racism and intolerance, Trump on Mexicans, Muslim people, southern border wall).

In this way Trump’s foreign policies, inchoate as they are—most recently in an extended interview with the New York Times—mesh fairly well with elements of the Republican isolationist tradition of William Borah (R, ID) in the 1920s and 1930s and Robert Taft (R, OH) in the 1940s and early 1950s. Attempting to channel the popular will, Republican isolationists evoked rugged individualism and unilateralism, allowing them as elites to project a populist appeal. Hubris and a tacit optimism—that the U.S. can get along better by focusing inward, without many partners or friends—has been fundamental to such positions and to their attractiveness.

Political isolationism hearkens to Washington, Jefferson, and Monroe, as leading lights to guide U.S. foreign as well as domestic policy. Inherently exceptionalist, its many forms aim to “make America great” by putting “America First”—a label Trump embraces despite its pre-WWII anti-interventionist legacy. In Trumpian terms that means strong border controls and anti-immigration measures, a domestic economic focus, staying out of potential quagmires such as in Syria, and pulling back from costly commitments in Europe, Asia, and Africa.

It also means protectionist economics. This second strain of isolationism has been equally long-standing. Historically critics of foreign economic ties, especially those involving processes and policies of globalization, have tended to cast such bonds as an erosion of autonomy and self-sufficiency, which often leads them to protectionist isolationism. The camp supporting this viewpoint has been able to tap into populist sentiments most effectively at times of economic crisis. Of course there are obvious costs. Protectionist isolationism seems intensely inwardly focused, and frankly naïve in the midst of lucrative international trade, globalization, and in light of free market economic logic. Common sense reciprocity in international exchange—foreign export markets require significant import trade—is oddly absent in historical and contemporary protectionist assertions. Similarly, it is clear that elevated import tariffs lead to higher prices for consumers.

Yet what is fascinating in this moment is that Donald Trump’s aura as a businessman and his nation-building-begins-at-home arguments complicate the usual counters to his sort of neo-mercantilist protectionist trades policies. As Trump explains: “I know the outer world exists, and I'll be very cognizant of that, but at the same time, our country is disintegrating, large sections of it, especially in the inner cities.” And, like Bernie Sanders (also running on anti-free trade agreements, against the TPP and NAFTA), Trump notes the U.S. has been “bullied” into bad deals leading to further declines for working America. Both point out that since 1979, real earnings, adjusting for inflation, are up only 17 percent. Both cite as well the lack of prosecutions for Wall Street speculators who helped precipitate the Great Recession.

If we take Trump’s ideas seriously, and despite an apparent lack of historical knowledge, his rhetoric matches an “angry” electorate’s limited demands for economic justice as well as a neo-mercantilist economic theory. Thus, he argues that American jobs have been outsourced abroad or been taken by low-wage workers (by which he means undocumented immigrants). As a solution, though the details are sketchy, Trump builds on the premise that enhanced export trade will generate wealth, that imports should be minimized, and barriers raised. This entails three objectives: to keep higher-wage jobs in the U.S.; to protect American industries; to enhance national self-sufficiency.

From infrastructure development to new job growth, shot through with xenophobia and exceptionalism, this is a populist isolationism that has legs because of its protectionism.

One of the major focuses of past protectionist arguments has been the effort to secure higher import tariffs to protect American domestic production. In the late nineteenth century, shielding nascent domestic industries from foreign competition by taxing imports was central to U.S. industrialization. It was also part of an international movement that saw tariffs as advanced political economics.

In November Trump put forward a proposed trade policy with China that hit all the high notes of protectionist isolationism. First, he highlighted the claim that China is a trade enemy, not playing fair—and that it’s acting as a “currency manipulator.” Second, he argued for unilaterally enforcing international patent law. Third, he pushed for ending China's “illegal export subsidies.” How could this be done? He later explained: it would be through a tariff! Trump suggested imposing a 45% tax on Chinese imports.

Such proposals have often been popular with Main Street Americans. In the U.S., similar policies continued through the early 1930s. The most notable example was the disastrous Smoot-Hawley tariff, which increased fees on thousands of imports in 1930. Intended to protect U.S. businesses and labor from the ravages of the Depression, that tariff had the opposite effect. It further contracted international trade and led to further trade conflicts. However, protectionist isolationism by the 1930s—blending tariff policy, xenophobia, and retrenchment from foreign interventions, alliances, and diplomacy—did not work in the short or the long run. Similar policies, however, continued to have traction in times of economic distress, such as the late 1970s in the wake of Vietnam and in light of the oil crisis and stagflation.

Trump’s pledges—such as penalizing U.S. firms that move their production facilities oversees or making South Korea, Japan, and Germany shoulder more of the expenses for U.S. military presence and operations—combine economic and diplomatic policy. Their widespread appeal has perplexed many, including party elites. It should not. However vague and conflicting, Trump’s intersecting foreign and domestic policies connect in terms of isolationist protectionism.

The relevance and rising appeal of such ideas is part of a decade-long pattern. Trump summed it up succinctly: “at some point … we cannot be the policeman of the world.” Americans, especially elected officials on the right, have been becoming more isolationist since at least 2004. National polls and the statements of GOP presidential hopefuls reveal a widespread insistence that the U.S. pull back from its global commitments to shore up the domestic economy and national security. Overarching all of this, according to Pew and Gallup polls, roughly 50 percent of Americans think the U.S. should “mind its own business” internationally. Take for example vigorous calls by Republicans for slashing funding for the State Department and diplomacy, cutting foreign aid, and engaging in fewer commitments not just in warzones but also in relief operations around the world. Even candidates like Ted Cruz who argue for heightened intervention against ISIS do so with the caveat “and then get the heck out.”

One thing is clear: a war-and-foreign-commitment-weary public is eager to focus on apparent vital national interests: job growth and keeping business at home; border and national security in a time of international threat; and a unilateral approach to getting what Trump calls “the best deals” at home and abroad. Although this protectionist isolationism has always been with us, it’s an empty promise.