AP Photo/Eric Gay Immigrant rights marchers in downtown Austin, heading to the Texas Capitol I n January of this year, organizers of the first Women’s March on Washington, D.C., organized a mass rally entitled “Power to the Polls”—in Las Vegas, Nevada. The event promised to take the anti-Trump fervor of Women’s March participants across the country into battleground congressional races. This second Women’s March came on the heels of Democrat Doug Jones’s victory in the December 2017 Senate race in Alabama, which has led to both high hopes and intense speculation about the Democrats’ 2018 prospects. Was that triumph a one-off outcome due to a spectacularly bad Republican candidate—you don’t often get to run against a credibly accused child molester—or is there a new opportunity to make progress in some of the reddest states in America? The most optimistic analysts have suggested the latter, with some finding inspiration in the Jones campaign’s massive mobilization of the black vote,...