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, accusing 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.

“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.”