But in the selection of their 2020 presidential nominee, Democrats will face a genuine crossroads. Few, if any, potential candidates would be equally effective at both energizing the party base and reassuring swing voters. Candidates who tilt mostly toward reassurance might include former Vice President Joe Biden, Colorado Governor John Hickenlooper, and New York Governor Andrew Cuomo. Those best positioned to mobilize could include Senators Kamala Harris of California and Cory Booker of New Jersey, two younger lawmakers who embody the party’s growing racial diversity, as well as Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts, two graying lions of the left.

Among Democratic political professionals, there’s probably a narrow majority that favors focusing on ordinarily Republican-leaning voters repulsed by Trump. However, the LA immigration rally was revealing because it showed the potential strength of the alternative strategy of mobilization.