Will 2020 be the political year of the millennial? It ought to be. Some 27% of next year’s electorate will belong to that generation, born between 1981 and 1996—almost exactly matched with the 28% comprised of baby boomers (1946-64). The oldest of us—I was born in 1982—are eligible to run for the presidency. Rep. Tulsi Gabbard, 38, and Mayor Pete Buttigieg, 37, are doing so.

Millennials will probably have to wait to enter the White House, but we’re making our influence felt. Presidential hopefuls like Elizabeth Warren are...