In the world of political advertising, what's one way to find out what your opponent is up to?

Search the classified pages.

On March 14, the Koch-backed public relations group, In Pursuit Of, placed an ad on an acting jobs website looking for a Caucasian actress age 50 to 60, white with red hair, light completxon and light eyes, according to a screen shot of the listing sent to NBC News by a source. The actress needed to be comfortable with a political ad about "tax reform and how a politician turned their back on voters." The listing says the actor's face will not be shown.

Less than one week later, another Koch-backed group, Americans for Prosperity, released an advertisement attacking North Dakota Democrat, Sen. Heidi Heitkamp, for her vote against the tax bill. Heitkamp is running for her second term in a red state that President Donald Trump won in 2016.

In the ad, a Heitkamp body double, whose face was never fully shown, walked through the halls of the Russell Senate office building. "When Heidi had the chance to help us with real tax cuts, she turned her back, voted 'no,’” the narrator said. 

Advertising for actors for political ads is not an anomaly. And neither is a campaign staffer scouring the classifieds for potential clues about what political ads might be coming down the pipeline. 

The same job listing also is looking for a 50 to 60 year-old white man with a slender body type around six feet tall with “peppered hair, a strong jawline, darker skin tone” for a similar ad. Perhaps it's for an upcoming ad for Democratic Sen. Joe Manchin of West Virginia? Or maybe Pennsylvania Senator Bob Casey? Maybe even Sen. Martin Heinrich of New Mexico.

Bets are on Manchin. He has the toughest race of the three.