Mr. Konczal laid out four hallmarks. You might be a social democrat if you support: a mixed economy, that is, a combination of private enterprise and government spending; social insurance programs that support the old and the poor; a Keynesian economic policy of government borrowing and spending to offset economic recessions; and democratic participation in government and the workplace.

If that’s what social democracy is, it’s not obvious what the term would add to the American political lexicon. Most Democrats would tell you they support all four of those things. So would quite a few Republicans.

Mr. Sanders said on the campaign trail this week that police and fire departments are “socialist institutions,” as are public libraries. He noted that Social Security and Medicare, which are very popular with Americans, are “socialist programs.” This, again, is more confusing than clarifying. If supporting Social Security and public firefighting makes you a social democrat, the term does nothing to distinguish Mr. Sanders from his opponents.

“When you look at the policies, there’s a way to see it as Bernie has cranked up Hillary’s agenda to 11,” Mr. Konczal said. To wit: Mrs. Clinton favors preserving Social Security with some enhancements for the poorest beneficiaries, while he wants to raise taxes on the rich to expand it in ways that could add $65 per month to the average benefit. This, like most political debates, is a disagreement about how far to turn the knobs when adjusting policy; it does not seem to call for a separate ideological label.

That said, Mr. Konczal did offer one difference between Mr. Sanders’s and Mrs. Clinton’s worldviews that is of kind rather than degree. This is decommodification: the idea that some goods and services are so important that they ought to be removed from the market economy altogether.

The idea behind the Affordable Care Act, and behind Mrs. Clinton’s approach to tinkering with Obamacare, is that quality health insurance should be affordable to everyone, and that people who can’t afford it should be given subsidies to buy it. For a democratic socialist, that’s not good enough; instead, health care should simply be provided to everyone without charge, removing the profit motive from health care.