The Associated Press this week traveled to rural Clinton County, a land where neither Joe Sestak nor Pat Toomey visits much but has been inundated with advertising -- like the rest of the state -- on the Senate race. In this heated race, AP's Marc Levy and Philip Elliott write, gobs of money are being spent on television ads in which each one casts the other as an extremist.

MILL HALL, Pa. — For many in this stretch of rolling forests, small towns and dairy farms, images of the two U.S. Senate candidates are shaped by the steady stream of television commercials that cast Democrat Joe Sestak and Republican Pat Toomey as extremists who are wrecking the economy.

Voters know almost nothing else about the candidates, both of whom live a four-hour drive away and seldom pass through the expansive north-central Pennsylvania corridor.

"You can't miss it with all the ads on TV," said Lynn Maryott, a registered Republican who recently retired from a joist manufacturer.

As he sat down to a bowl of oatmeal at a roadside restaurant in Mill Hall, Maryott said what many voters in the nation's sixth most-populated state are thinking.

"It makes you wonder where all that money comes from," he grumbled.

National party committees and interest groups have already made Pennsylvania a priority. Its Senate race may predict how the state will swing in the 2012 presidential election, which is why President Barack Obama, who backed Sestak's primary opponent, is heading to Philadelphia on Monday to raise money for Sestak.

If Obama's fellow Democrats are to keep their majority in the Senate, this is a seat they must win. But it might not be cheap: Republican Rick Santorum and Democrat Bob Casey alone spent $46 million in Pennsylvania's fierce race for Senate in 2006, which Casey won.

Based on federal election filings and campaign estimates, Sestak and Toomey thus far haven't spent close to half that amount.

Money is again flowing into the state — estimates from the campaigns suggest that outside groups, including the U.S. Chamber of Commerce, the Club for Growth and the Democratic Senatorial Campaign Committee, have already spent $6 million to $7 million on TV ads since July.

The airwaves carry the message that Toomey is to blame for the economic meltdown, that Sestak is recklessly raising taxes and the national debt. With the balance of power in Washington at stake — and airtime inexpensive here in rural Pennsylvania — there's little wonder the ads have become so aggressive and plentiful.

The full story is here, a good overview of the race.