After a year of self-flagellation and angst, Democrats finally got some good news last week. But they shouldn’t get carried away: They also got some bad news.

First the bad news: Rural America still really dislikes Democrats. But that wasn’t a surprise. The good news came in increasingly affluent and diverse Virginia: In the age of Trump, well-educated suburbanites like Democrats considerably more than they used to. And voters are, overall, quite energized (turnout was at a 20-year high for the Virginia governor’s race) — especially younger voters, who supported the Democrat, Ralph Northam, overwhelmingly as compared with the Democratic nominee in 2013 and turned out at much higher rates.

All this, despite Democrats’ nationally failing to coalesce around a singular bold message and Mr. Northam’s running a decent but not particularly inspiring campaign.

Democrats are benefiting from a law of political physics, and despite so much else going haywire in our politics, it appears to still hold: There is a pendulum-like swing in American politics against the party that holds the presidency. One of the most striking results from the exit polls is that Mr. Northam did a little better across almost all subgroups in Virginia than Hillary Clinton did in 2016.