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.”