The little-noticed battle for Pennsylvania's contested U.S. Senate seat is getting more attention, now that Republican challenger Tom Smith has gained on incumbent Democrat Bob Casey.

And Casey's begun fighting back, attacking Smith in the ad above with a statewide TV buy.

Casey has the advantages of incumbency and a revered Pennsylvania name, so polls have long showed him with big leads. But Smith has been hammering away with TV ads such as the one below.

Smith has put more than $7 million into his own campaign, and those ads have had an effect.

Recent polls show Smith pulling to within five to 10 points of Casey. Muhlenberg College political scientist Christopher Borick says Smith has made it a race.

"It may still be that he is still the underdog in this race," Borick said in an interview. "But now he's an underdog with a chance, as compared to an afterthought."

Casey's campaign has been relatively quiet until recently, holding few public appearances and refraining from TV advertising.

Casey's campaign manager, Larry Smar, said it doesn't make sense to schedule a lot of news conferences when the media aren't particularly interested in covering the race.

It's also an old political strategy for an incumbent not to give a little-known opponent publicity by calling attention to a race.

And Borick said Casey's campaign was likely saving cash for ad buys late in the campaign.

Now that it's October, Casey is attacking his opponent as "Tea Party Tom."

Casey's ad asserts that "Tom Smith's plan would give millionaires like himself a $250,000 tax break, while the average middle class family would get a $2,000 tax increase."

Information supplied by the Casey campaign to support the claims refers to two analyses done by the fact-checking site PolitiFact. But both are reviews not of Smith's campaign platform, but of Mitt Romney's tax proposals. Read them here and here.

Smith recently unveiled his own proposal for a flat tax, but he hasn't specified rates or other details, so it's not clear what its impact would be.

Smar noted, as the Casey material does, that Smith in a July appearance declined to cite a specific difference between his fiscal views and Romney's, associating him with the Romney perspective.

There are no debates scheduled, but it's clear the ad wars will continue. And Smith, who has personally funded 85 percent of his campaign spending, seems ready to put plenty more cash into the race before it's over.