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That single ad ran at least 14 times during the two-hour window.

Sen. Sherrod Brown, the incumbent Democrat, and state Treasurer Josh Mandel, the Republican challenger, and their allies ran more than 20 commercials over that same time frame.

In his ads, Mr. Brown touts Mr. Mandel’s opposition to the auto bailout and casts him as a pawn for shady right-wing figures.

Mr. Mandel juxtaposed news reports that said Mr. Brown has been “delinquent” in paying his taxes against his willingness to support tax hikes and vote for congressional pay raises.

Meanwhile, Crossroads GPS, the super PAC affiliated with Karl Rove, who served as a top adviser to President George W. Bush, is attacking Mr. Brown, and the Democratic Senatorial Campaign Committee is running ads against Mr. Mandel.

Topping it off, the local newscasts also spent much of their time covering the races, giving viewers little respite.

The ads underscore the importance of Cincinnati and surrounding Hamilton County, which are some of the biggest prizes up for grabs in Ohio. The state is considered in play in the presidential and Senate elections this year.

For decades, the area was a Republican stronghold, serving as a counterbalance to urban, more traditionally Democratic parts of the state.

But Mr. Obama’s victory here four years ago changed that. Now both parties say they are optimistic that they will capture the county.

This year, Democrats say they got a head start in the area, thanks to heavy investments the Obama campaign made during the summer, running ads aimed at defining Mr. Romney as a corporate raider, said Caleb Faux, Hamilton County Democratic Party executive director.

He also said the Obama camp has had at least one full-time staffer on the ground here coordinating with volunteers since the 2008 campaign and has had eight campaign offices open for months.

“We started sooner, and we also have a larger and better-organized ground game than we saw in 2008,” Mr. Faux said. “A good, solid, ground game can make a solid difference of 2 to 4 points. I think the investment of the Obama campaign in that ground game is huge, and I think that will pay off.”

Republicans, though, say they’re on the ground now and have a much better financial footing than they did four years ago, when Republican nominee John McCain was hamstrung by the public financing system, while Mr. Obama was not. This year, Mr. Romney joined Mr. Obama in forgoing public funds, freeing both men to raise and spend without limits.