In 1898, the first election in which Milwaukee’s socialists ran their own candidates, the party’s mayoral candidate won 5 percent of the vote. But the public’s rising disgust with corruption in the Democratic administration of Mayor David Rose led to steady and significant gains for the socialists, and in 1910 they won 21 of 35 City Council seats, 14 state legislative seats and the mayor’s office. That year, Victor Berger also became the first socialist elected to Congress.

There was no need to go on a “listening tour” to find out what the working class wanted, since so many of the party’s newly elected officials were workers themselves, including the new mayor of Milwaukee, a woodcarver named Emil Seidel. The eldest of 11 children, Seidel had been forced to go to work after grammar school. He and his fellow socialists in city government — including his personal secretary, the poet Carl Sandburg — instituted dozens of measures to improve their constituents’ lives.

They installed hundreds of drinking fountains, prosecuted restaurateurs for serving tainted food and compelled factory owners to put in heating systems and toilets. Most significantly, Seidel appointed an aggressive new health commissioner, whose department oversaw a reduction of more than 40 percent in the number of cases of the six leading contagious diseases, among them scarlet fever, whooping cough and smallpox, within two years.

The most widely admired trait of the sewer socialists was their integrity. “They never were approached by the lobbyists, because the lobbyists knew it was not possible to influence these men,” William Evjue, a Republican assemblyman, said of his socialist colleagues. Chicago, 80 miles to the south, was awash in corruption for decades, while Seidel’s administration had largely cleaned up Milwaukee’s municipal government in its brief run. But Democrats and Republicans joined forces to run a single candidate against Seidel, and he and most of the city’s elected socialists were defeated in 1912. (Later that year, when Debs ran for president, Seidel was his running mate, helping the Socialist Party win 6 percent of the vote, its highest percentage ever.)

One Milwaukee socialist who survived, however, was Daniel Hoan, the city attorney, who was not up for re-election that year. In 1916, Hoan avenged the socialists’ losses by winning the mayor’s office, which he held until 1940. Hoan oversaw further public investment, including the construction of the nation’s first public housing project, Garden Homes.

During Hoan’s tenure, an urban planner named Charles Whitnall designed sewer socialism’s most enduring achievement: the Milwaukee County park system, one of the most extensive and acclaimed in the country. The city added miles of new parkland along Lake Michigan’s waterfront, which had been dominated by private mansions.

Hoan adhered to sewer socialism’s tradition of spending taxpayer money frugally. “The objective is to give the best government possible,” Hoan once said. “But not necessarily at a low tax rate — at the lowest cost that can be paid.” During the Depression, he created a voluntary program in which city employees, including Hoan, took a 10 percent pay cut to fund public works projects that put nearly 15,000 unemployed people to work.