The Democrats Have Had This Primary Before

The problem with campaigning on electability is that it’s a brittle rationale for a candidacy compared with organic support from the grassroots.

As of this writing, the Democratic presidential contest looks very fluid, with four candidates bunched up in Iowa and New Hampshire. But the sudden relevance of foreign policy, thanks to the confrontation with Iran, has made it look more and more like a two-person race between Joe Biden and Bernie Sanders.

Both candidates think the issue helps them, and they’re probably right. Biden’s foreign-policy experience and comparative hawkishness...