While Brown has highlighted his vote in Congress against authorizing the Iraq war, the race has been just as much about the economy, with Brown emphasizing his opposition to free-trade agreements. Whereas polls in most states show Iraq to be the top concern for voters this year, polls in the Buckeye State show that the economy is an even higher concern.

"Brown is running as an economic populist and as a fighter for the middle class," says Herb Asher, a political science professor emeritus at Ohio State University. "It might not play as well in other states where the economy is doing better, but we've lost a couple hundred thousand manufacturing jobs, some of the best-paying jobs in the state. That resonates."

DeWine, a moderate Republican who has stressed his record of bipartisanship in the U.S. Senate, began this year's campaign with ads that billed him as "an independent fighter for Ohio families." But as Brown maintained a commanding lead in the polls, DeWine has produced more-negative ads, including its most recent, which accuses Brown of promoting an office worker implicated in a drug bust more than 20 years ago. "He's had to go more and more negative," says Asher. "That's undermined his image as a thoughtful independent who reaches across the aisle."

Early last month, the Republican Party appeared to acknowledge that it might be headed for defeat in Ohio, as it poured more money into competitive Senate races in Missouri, Virginia, and Tennessee.

"Sherrod Brown is one of the most liberal members of Congress," says National Republican Senatorial Committee spokesman Dan Ronayne. "If he were to defeat somebody who fits the state as well as DeWine does, it would tell us that there were greater forces at work there."

—Dan Gilgoff