Source: https://www.vox.com/policy-and-politics/2018/3/14/17109448/pennsylvania-special-election-conor-lamb-defeats-rick-saccone

The seat had since 2003 been held by Republican Rep. Tim Murphy, who was so secure in his seat that he often failed to attract a Democratic challenger. Murphy suddenly resigned in October amid revelations that he had pressured a woman with whom he was having an extramarital affair to have an abortion.

But even after he stepped down, national Democrats didn’t think they could compete in the special election, one Democratic Congressional Campaign Committee (DCCC) operative told Vox.

That was until Conor Lamb came along.