This district should be no problem for Republicans to hang onto. Pennsylvania Republicans gerrymandered the 18th District to combine GOP-leaning Pittsburgh suburbs with once-Democratic mill towns and rural areas that have trended steadily more Republican in recent national elections. Tim Murphy, the Republican incumbent, ran unopposed in 2014 and 2016, and Trump won the district by a whopping 20 percentage points.

But the special election clearly has Republicans on edge.

Lamb is competing with Republican Rick Saccone, a 59-year-old state representative and former military intelligence officer. Murphy had held the seat comfortably since 2003, but resigned in October after it emerged that the anti-abortion congressman had asked a woman with whom he was having an extramarital affair to have an abortion.

Democrats have had a string of victories since Trump’s inauguration. In fact, they’ve flipped 34 state legislative seats, one governor’s seat and one U.S. Senate seat from red to blue. Republicans, meanwhile, have only picked up four state legislative seats.