Click here to watch "The Subject."

The bitter back-and-forth between Barack Obama and John McCain continued this morning as each candidate released a TV ad accusing the other of dishonest attacks, setting a contentious tone for tonight's presidential debate in Nashville, Tenn.

Obama's spot, "The Subject" (subscription), echoes an ad (subscription) released yesterday in denouncing McCain's efforts to shift attention from the struggling economy. "He's out of ideas, out of touch and running out of time," the announcer says, portraying McCain as desperate, with the election clock winding down.

The spot goes on to claim that McCain has no solution for getting the country out of its current fiscal downturn, so he is turning to "smears." It also cites comments from an unidentified McCain adviser who told the New York Daily News on Monday: "If we keep talking about the economic crisis, we're going to lose." The ad appeals to voters who are suffering as they "lose their jobs, homes and savings" and insists that "it's time for a president who'll change the economy -- not change the subject."

With similarly harsh language, McCain goes after Obama's image as an above-the-fray politician and seeks to raise questions about what he stands for in "Hypo" (subscription). The spot opens with footage from a local TV news report in Missouri in which the reporter says the Obama campaign asked law enforcement officials to "target" anyone running misleading attack ads against the Democratic candidate. "How hypocritical," an announcer charges, citing reports that characterize several of Obama's ads as "falsehood[s]," and "not true." Obama "promised better," the announcer concludes. "He lied."

The candidates go into tonight's debate at Belmont University in Nashville with Obama holding a lead in national and battleground state polls.