Some thought those snowy protests would launch a Democratic surge in Wisconsin. Instead they appear to have marked the beginning of the party’s decline. Since 2011 Wisconsin Republicans have been on a winning streak.

In the state Assembly, Republicans enjoy their largest majority since 1957. Twenty of the 33 seats in the state Senate belong to the GOP, the most since 1970. Mr. Walker, who easily survived a recall election in 2012, won a new term in 2014. Last November voters rejected Democrat Russ Feingold’s bid to reclaim the Senate seat he lost in 2010 to Republican Ron Johnson. Remarkably, Donald Trump won Wisconsin’s 10 electoral votes—the first GOP presidential candidate to do so since Ronald Reagan in 1984.

The latest evidence of Democrats’ sorry slide is the election next Tuesday for a seat on Wisconsin’s Supreme Court. Only six years after their historic demonstrations against Act 10, Democrats couldn’t find a single candidate willing to run against conservative Justice Annette Ziegler in her bid for another 10-year term.

A spokesman for the state’s Democratic Party told the Milwaukee Journal Sentinel in January that “a number of people” considered opposing Justice Ziegler before ultimately deciding not to take the plunge. Considering Wisconsin’s political history as an incubator of 20th-century progressivism, this development is rather stunning. “The Democratic Party has done a terrible job,” Glendale Mayor Bryan Kennedy told the Journal Sentinel. “We haven’t built the kind of infrastructure that says to a Supreme Court candidate, ‘We can help you.’ ”