A Democratic political action committee has launched an expensive ad campaign targeting embattled GOP Rep. Scott DesJarlais (Tenn.), a physician who's come under fire this month for urging a former mistress – and patient – to have an abortion.

Sponsored by the House Majority PAC, the $100,000 campaign is the first indication that Democrats see DesJarlais as vulnerable in Tennessee's conservative 4th District. Before this week, the national party had not provided any financial support to Democratic state Sen. Eric Stewart, who's challenging DesJarlais's run at a second term.

The ad starts with a clip taken from a DesJarlais campaign ad – "As a doctor, Scott DesJarlais earned his patients' trust," the narrator says – before cutting away to a local news anchor covering last week's revelation that DesJarlais, who's running on an anti-abortion-rights platform, had urged a former mistress to undergo such a procedure.

"The pro-life supporter had an affair with a patient a decade ago, and after learning she was pregnant, urged her to have an abortion," a WBIR newscaster says, referring to the story first reported by the Huffington Post.

Titled “Trust,” the weeklong ad buy begins airing Friday in the Nashville and Chattanooga markets.

DesJarlais, who survived scandalous details surrounding a decade-old divorce to unseat former Rep. Lincoln Davis (D) in 2010, has been the heavy favorite to keep his seat in November.

But poll numbers released by Stewart's campaign Wednesday suggest the recent abortion scandal is taking a toll, indicating the Democrat has pulled to within five points since the news broke.

"The plates have moved and this has become an extremely competitive race," Andrew Myers, who heads Myers Research, a Virginia-based Democratic polling firm, said Wednesday in announcing the figures. "In fact, it's a dead heat today."

Stewart's campaign has declined to release the full poll results, which leaves the challenger wide open to charges that he's cherry-picking only the advantageous numbers. Still, the House Majority PAC's new ad campaign is evidence the Democrats see a potential pick-up opportunity stemming from DesJarlais's troubles.