Related coverage Santorum, Casey tussle in radio debate On the Internet Watch KYW-TV video from this morning's radio debate in Philadelphia See WPVI-TV's Web site for coverage of tonight's debate at 7 p.m.

U.S. Sen. Rick Santorum and challenger Bob Casey meet twice today for what are expected to be the final debates of their long campaign. They offer what may be the last clear opportunity to shift political dynamics that seem to have settled into an ominous equilibrium for the Republican incumbent.

Mr. Santorum's need to change the status quo was obvious Thursday in the first of three closely spaced face-offs ushering in the final three weeks of a 20-month campaign. Neither candidate won points for civility in the hourlong session in KDKA's studios, but it was clear that Mr. Santorum was the consistent aggressor and Mr. Casey more often the counter-puncher.

This was arguably the most watched Senate race in the nation when the election season began, but the suspense has been blunted by months in which polls have depicted a flat line of support for the incumbent at the 40 percent level.

"It's always hard for an incumbent to pick up the undecided," said Brad Coker, managing director for Mason-Dixon Polling & Research. "Once they sink into the 40s they tend to stay there. Minus a big mistake by Casey it's probably next to impossible."

After weeks of bad news for Republicans nationally, from the streets of Iraq to the House page controversy, Mr. Santorum is "swimming against the tide in so many ways right now," Mr. Coker said.

Perhaps Mr. Santorum's best chance of profiting from a Casey gaffe would come by goading him into one. That tactic was on display throughout the cut and thrust of Thursday afternoon. The Republican had success with a couple of gotcha questions: Mr. Casey couldn't name the former president of Iran or the percentage of state stock investments in companies on Lou Dobbs of CNN's list of those who outsource U.S. jobs overseas. But nothing emerged from the 60 minutes that seemed likely to be remembered as a turning point in their fight.

Mr. Santorum will be looking for more opportunities this morning as he and Mr. Casey exchange views and -- if last week is any guide -- insults for 60 minutes of radio beamed at commuters in the Delaware Valley. In the evening they will resume their combat on television before a panel of journalists. Television is traditionally the more powerful medium but the drive-time radio session gives both candidates a chance to reach commuters with a more casual interest in politics.

John Brabender, Mr. Santorum's veteran media strategist, said the relative impact of debates can loom larger than the ubiquitous TV ads in the final days of a campaign.

"Let's face it, they're going to run good TV and we're going to run good TV; maybe you can move a point or two but after a while we tend to drown each other out. ... Having Casey and Santorum going toe-to-toe is important."

Fund raising is one area in which the incumbent has enjoyed an advantage throughout the campaign. Whether what has been a 2-to-1 Santorum advantage persists will also be known today. The latest campaign contribution reports were due over the weekend. The Casey campaign said it had $3.7 million in cash on hand on Sept. 30, at the end of the latest reporting period. Mr. Santorum's campaign said it would disclose his report today.

Mr. Brabender argued against the notion that the relatively constant poll numbers were likely to persist.

"A big part of this race has been almost directly tied to a generic [congressional preference] ballot and the president's numbers in the polls," he said. "That's common until you get to the end of an election and when people begin to focus and say this is not a national election, this is a Pennsylvania election."

His colleague, Santorum press secretary Virginia Davis, stressed the debates' importance with a return to the campaign's frequent charge that Mr. Casey has tried to run out the campaign clock without offering detailed positions on issues. The debates, she said, offered a chance to break that pattern.

Her opposite number, Larry Smar, disagreed.

"This has been part of the Santorum talking points for the last year and it's simply not true. He's campaigned all over the state. He's campaigning all weekend. That's why we re-issued the position papers we've put out throughout the campaign.

"Bob Casey has said what he's going to do and it's not more of the same, which is all that Sen. Santorum offers."

The debates tomorrow will be in Philadelphia, the state's biggest media market and one that, with roughly 40 percent of the state's voters, is crucial to the outcome of any statewide race.

The city neighborhoods radiating from the debate sites, close together in Center City, are reliably Democratic, and the Philadelphia suburbs, though still dominated by registered Republicans, have been increasingly hospitable to Democrats in recent elections. In Mr. Santorum's last election, when he won his second term against former U.S. Rep. Ron Klink, voters from those counties split their ballots, producing comfortable majorities for the senator while President Bush was losing them to former Vice President Al Gore.

Recent polls, however, have shown significant deficits for Mr. Santorum in those bedroom counties. Mr. Coker said that his latest Mason-Dixon survey showed Mr. Casey leading in that region, 52 percent to 36 percent.

Mr. Brabender said he was confident that his candidate would hold those counties when the ballots are cast on Nov. 7. "What happens with the Republicans out there, they swing their votes on two issues -- guns and abortion -- and Casey has the same position [as Mr. Santorum]."

But Mr. Coker noted that his numbers seemed to show that the swing voter effect was working in the Democrat's direction.

In his latest Pennsylvania survey, late last month, Mr. Casey was winning 14 percent of Republican voters while Mr. Santorum, who historically has had strong appeal to conservative Democrats, was winning only nine percent of Democrats. That, he said, was the opposite of a national trend that came with the rise of the Reagan Democrat, one in which Republican candidates have typically done better at shearing off Democratic votes than Democrats have done among GOP voters.

"That's a trend around the country that's killing the Republicans in state after state," he said. "Registered Democrats are staying with their guy this time."