In a district that one independent analyst, Keith Haller, refers to as “the fertile crescent of American politics,” the race has made for unusual conversation on the campaign trail. “I’ve gone door to door,” said Marshall Cohen, the campaign manager for Jamie Raskin, the state senator, “and people ask, ‘What’s your cash on hand?’ ”

Here in Chevy Chase, Kathleen Matthews, the former television reporter, held a meet-and-greet for voters last week in the home of Jen Burton, a Democratic media strategist. Ms. Burton says her jaw dropped recently when slick brochures sent by David J. Trone, the wealthy businessman candidate, started arriving in the mail.

“I was like, ‘Oh my God,’ ” she said. “His direct-mail consultant is making a killing.’ ”

For months, the race seemed a neck-and-neck contest between Mr. Raskin, 53, a full-time constitutional law professor at American University backed by many in Maryland’s Democratic establishment, and Ms. Matthews, 62, who left TV reporting a decade ago to join Marriott, the hotel chain. He has a string of legislative accomplishments in Annapolis; she is well known from her 25 years on air at the ABC affiliate here.

Between them, they have raised nearly $3 million. Mr. Raskin’s donor list is heavy with lawyers and professors; Ms. Matthews’s includes an array of Washington movers and shakers (including some, Raskin backers grumble, who have appeared as guests on her husband’s show).

Then last month, one week before the filing deadline for candidates, in waltzed Mr. Trone.

Mr. Trone, 60, is the co-owner (with his brother Robert) of Total Wine & More, the nation’s largest independent wine retailer, and a philanthropist who recently donated $15 million to the American Civil Liberties Union to promote criminal justice reform. He also donates handsomely to politicians (including Republicans in states where his company does business), and in November hosted President Obama at his Potomac, Md., home for a $20,000-a-couple dinner to benefit Democrats.

The fund-raiser produced one of those off-the-cuff moments that potential candidates dream of: a cellphone video of Mr. Obama saying of Mr. Trone, “We can run him for something.” Naturally, Mr. Trone made it into an Internet ad. Ms. Matthews, calling it misleading, demanded he take it down. (He has not.)