Dorset, Vt.

The gruff, unkempt Vermonter is knocking them dead. Campaigning for the Democratic Party’s presidential nomination, Bernie Sanders is packing houses, making headlines and putting a scare into Hillary Clinton supporters. This despite his being 73 years old and not even a Democrat.

Sen. Sanders, a self-described democratic socialist, is the junior senator from Vermont, the state that could plausibly claim the title of the most progressive in the union. Whatever the cause du jour—gay rights, a $15 minimum wage, labeling genetically modified foods—Vermont can be counted on to be near the front of the parade.

The Vermont Progressive Party, running alongside the Democrats and Republicans, has held seats in the state legislature since 1991. A decade ago, resolutions for the impeachment of President George W. Bush were introduced at several town meetings and debated along with matters like leash laws for dogs and the funding of snowplows.

Progressives here take pride in being a kind of vanguard, showing the way for the rest of the nation. Mr. Sanders did much to incubate this spirit in the 1980s as mayor of Burlington, the state’s largest city, by raising taxes on businesses, instituting affordable-housing programs, and initiating cultural events to include poetry readings by Allen Ginsberg and speeches by Noam Chomsky. So as Mr. Sanders makes his case for taking the progressive agenda nationwide, it is interesting to consider how that agenda is doing in Vermont