This election cycle, two candidates have dared to touch a third rail in American politics.

Not Social Security reform. Not Medicare. Not ethanol subsidies. The shibboleth that politicians are suddenly willing to discuss is the idea that America might have something to learn from other countries.

The most notable example is Bernie Sanders, who renewed his praise for Western Europe in a recent interview with Ezra Klein. “Where is the UK? Where is France? Germany is the economic powerhouse in Europe,” Sanders said. “They provide health care to all of their people, they provide free college education to their kids.”

On ABC’s This Week in May, George Stephanopoulos asked Sanders about this sort of rhetoric. “I can hear the Republican attack ad right now: ‘He wants American to look more like Scandinavia,’” the host said. Sanders didn’t flinch:

That's right. That's right. And what's wrong with that? What's wrong when you have more income and wealth equality? What's wrong when they have a stronger middle class in many ways than we do, higher minimum wage than we do, and they are stronger on the environment than we do? Look, the fact of the matter is, we do a lot in our country, which is good, but we can learn from other countries.

Democratic politicians, and especially the furthest-left ones like Sanders, have always been more open to the Scandinavian example than others—but it’s been a long time since anyone so liberal has achieved Sanders’s prominence nationally. It’s especially unusual for any Republican to follow suit, but Jeb Bush did just that when he returned from a jaunt to Europe, marveling at technological innovation in government services: “You can fill out your tax return in Estonia online in five minutes.”

These statements are particularly unusual in the recent scope of American politics. In an age when the totemic invocation of American exceptionalism (a phrase, it’s worth recalling, invented by Joseph Stalin, and sometimes attributed to his fellow non-American Alexis de Tocqueville) has become a political necessity, it’s no surprise that politicians generally avoid citing foreign models.

Supreme Court justices, who at least like to pretend they’re not part of the political system, have given in to temptation. Former Justice Sandra Day O’Connor predicted, “Over time we will rely increasingly, or take notice at least increasingly, of international and foreign courts in examining domestic issues.” Justices Stephen Breyer and Anthony Kennedy and retired Justice John Paul Stevens have all cited foreign laws in opinions. They’ve been met with anger and criticism from both Republican lawmakers and conservative colleagues on the Court.

During the debate over healthcare reform, President Obama and Democrats who supported the law strenuously labored to make their overhaul market-based, and to avoid proposing a “European-style” universal healthcare system. Republicans, however, labeled Obama a socialist, accused him of trying to turn the U.S. into a European welfare state. They were quick to draw comparisons with Europe—unflattering, and often exaggerated, ones, of course. (Europeans themselves were perplexed by the whole proceeding.)

There are exceptions to this rule. Israel is generally a safe example, of both tech innovation and of security procedures. Praising Communist China’s results in efficiency and education—though not the methods—is doable. Some conservatives have gone so far as to praise Russian President Vladimir Putin, contrasting him with Obama as someone who gets stuff done. As Rudy Giuliani discovered when he made such a comment, the fact that Putin’s leadership rests on political repression and military aggression means it’s an unwise model to use.

This intellectual xenophobia is, in the grand scheme of American history, a relatively new phenomenon, Daniel Rodgers notes. Rodgers, who is professor emeritus of history at Princeton and the author of Atlantic Crossings, a history of America’s international connections before World War II, points out that the U.S. was shaped early on by foreign borrowings. Not only was the nation founded philosophically on the thought of the Englishman John Locke, but the industrial revolution stateside was set off in part by Samuel Slater’s importation of mill design from the U.K. (The designs were protected intellectual property; Slater memorized as best he could, sparking an explosion of innovation.)  

“It’s impossible to think about American capitalism without thinking about borrowed and appropriated technologies,” Rodgers says.

The intellectual exchange reached a high point in the late 19th and early 20th centuries. Many American elites saw themselves on a journey toward industrialization, alongside Western Europe.  

“The genius of America for those progressives was to be wise and thoughtful and smart in extracting the best from this whole world of experience, adapting it to American conditions and American political realities, and making it work,” Rodgers says. In particular, Theodore Roosevelt was “unabashed” about “gleaning the best that the world had to offer for incorporation into the American social, political, and cultural systems.”

The major turning point came in 1945.

“The Americans came out of the Second World War with a sense that there was no country like them,” Rodgers says. “They imagined they had won the Second World War all alone, as if the Soviet Union had nothing to do with it. When it was done, Western Europe was obliterated. They stood all alone in their own minds as the defenders of freedom.”

That’s where things stand today. But in a post-Cold War world, the increasingly strident repetition of “American exceptionalism” starts to seem more like a mantra for warding off an increasingly connected world, and one in which the U.S. doesn’t have a monopoly on good ideas. (The popularity of the phrase in the age of Obama is surely in part a result of discomfort caused, and sometimes outright bigotry inspired, by Obama's own international roots—the son of a Kenyan, raised partly in Indonesia.) In other words, the louder insistence on exceptionalism may actually herald a greater acceptance of foreign ideas.

Jeb Bush and Bernie Sanders may seem, at first glance, an unlikely duo to lead that charge. But who better to represent America’s capacity to absorb the best that other lands have to offer than the conservative scion of New England bluebloods who married a Mexican woman, and the socialist son of a Jewish immigrant father?