The latest installment: A 30-second spot from the Clinton campaign airing in North Carolina and Indiana, where voters go to the polls tomorrow.
"What's happened to Barack Obama?," an announcer asks as the spot opens. After a woman says she is living "paycheck to paycheck," he adds: "He's attacking Hillary's plan to give you a break on gas prices because he doesn't have one."
"Hillary wants the oil companies to pay for the gas tax this summer, so you don't have to," the announcer adds. "Barack Obama want you to keep paying – $8 billion in all. Hillary's the one who gets it."
The spot features a number of working class Americans talking about their economic challenges, and closes with a man saying "Hillary Clinton is the candidate that's going to fight for working people."
That's not the only negative ad out today. A group called Friends of the Earth Action, which has endorsed Obama, has released a Web ad saying Clinton is "pandering for votes and not telling the truth" on the gas tax issue. Watch here.
UPDATE: And the Obama campaign responds with a negative ad of its own, one that accuses Clinton of "the same old negative politics." In the spot, an announcer tells viewers that Clinton's hometown newspaper (The New York Times) "says she's taking the low road":