But in the final years of the 19th century, a sudden burst of young people demanded new issues — their issues. Tired of, as one Coloradan put it, “rotten old hulks who monopolize the offices and dwell upon the past,” a generation of young men and women denounced their leaders and with them, partisanship. They demanded political reform, labor reform and social reform, and declared that they would withhold their votes from any party that didn’t respond. “The ratio of party feeling and self-interest is rapidly changing,” declared one sharp-tongued New Yorker in 1898, adding that “the younger generation hates both parties equally.”

Politicians saw the change and chased after those young voters. Soon, The Washington Post was begging: “Don’t sneer at them as ‘boys,’ when they drop into your ward meetings, don’t make them do all the work of the campaign.”

In the new century, young people’s “self interest” helped kill extreme polarization by forcing both parties to pursue the same set of demands. Youthful independent voters emerged as a decisive third force, with just enough influence to swing close elections. Politicians scrambled after them, beginning the Progressive Era, passing laws protecting workers, cleaning up cities and championing the young.