DesJarlais, a socially conservative congressman and doctor, has been beset by allegations that he had multiple affairs, supported his ex-wife's decision to have two abortions and prescribed drugs to one of the women he was having an affair with. He's said he won't resign.

The district is heavily Republican — DesJarlais won reelection by a double-digit margin despite some of the allegations coming out before the election — and he's much more vulnerable to a primary than general election challenge.