LOS ANGELES — President Trump was hanging out here in the land of earthquakes, but he was 2,500 miles away from the tremor that really shook his party on Tuesday night.
While the president hobnobbed with wealthy donors in the exclusive enclave of Beverly Park, the voters in the suburbs south of Pittsburgh were in revolt, giving the Democratic candidate a narrow lead in a special election in Pennsylvania that was taking on outsize proportions.
Just as they did outside Birmingham and Montgomery, Ala., in December, and Richmond, Va., and Washington, D.C., in November, energized and angry suburban voters were swamping the Trump stalwarts in the more rural parts of those regions, sending a clear message to Republicans around the country.
While Republican turnout in a district that Mr. Trump won by 20 percentage points was healthy, Democrats showed once again that they could tap unions and other traditionally friendly groups to get their voters out in droves. The N.A.A.C.P. helped win Attorney General Jeff Sessions’ Alabama Senate seat for Doug Jones in December. Organized labor, once seen as fractured and feckless in the Trump era, gave the Democrat Conor Lamb his lead in Pennsylvania overnight.
Rick Saccone, the Republican candidate who wrapped himself in Mr. Trump’s cloak and drew the president to his district last weekend in a bid to rescue a faltering campaign, trailed Mr. Lamb, a former Marine seeking to show his party can compete even in red territory. Mr. Lamb held a lead of just 641 votes early Wednesday, with some absentee ballots still to be counted, but Democrats went ahead and claimed victory.
Whether Mr. Lamb holds on to win the House seat matters less than the fact that he was so competitive in the first place. The rebuke of Mr. Trump came from a part of western Pennsylvania that overwhelmingly supported him in 2016 and that typically would not seem likely to turn to a Democrat. The district is seen as so strongly Republican that the Democrats did not even field a candidate in recent years.
And while Mr. Saccone carried the most Trump-supporting counties along the West Virginia border, Mr. Lamb made just enough inroads in those rural areas to give the voters in suburban Allegheny County the chance to deliver the Democrat the slimmest of leads.
The stinging message could hardly have been more…