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Good morning, and welcome to Election Day — at least in one congressional district, in southwestern Pennsylvania, which is holding a special election that feels like a referendum on President Trump.

The 18th district is a mix of coal country and Pittsburgh suburbs, and it leans strongly Republican. Both Trump in 2016 and Mitt Romney in 2012 won it by almost 20 percentage points. Yet the Democrat nonetheless has a real shot to win.

Why? Trump’s unpopularity is the main reason. But the strength of the Democratic candidate — Conor Lamb, a 33-year-old former Marine and prosecutor — also matters. He has run to the political middle on cultural issues (like guns and abortion) and to the left on economic ones (like trade).