It's a surprising turn for the GOP in a key swing state hard that has been hit by job losses and in which President Barack Obama's popularity has slipped.
Republicans last November swept to their biggest electoral success in Pennsylvania since 1994, in large part by blaming Democratic policies for the ailing economy.
The party picked up five U.S. House seats along with a fiercely contested Senate race as Pat Toomey beat Democrat Joe Sestak for Republican-turned-Democrat Arlen Specter's seat. The GOP also recaptured the governorship and control of both houses of the state Legislature.
As Labor Day nears and election season cranks up, Republicans said there's still plenty of time to find a major challenger against Casey, who won his seat in 2006 by a whopping 18-point margin and is seeking a second term in 2012.
"I'm still very bullish about next year," Rob Gleason, chairman of the Pennsylvania Republican Party, said in a recent telephone interview with The Associated Press. "We will have a top-flight candidate and we will conduct a vigorous campaign. I am confident that we will beat Senator Casey."
Casey said he "fully expects" to face a strong GOP challenger.
"It's a very competitive state, so I have to be prepared for a tough race," Casey told AP in a phone interview Thursday. "I can't control any of that, so I just prepare."
Gleason, who wasn't naming names, said a big-name challenger could emerge in November and still mount the kind of campaign needed to take down Casey. Gleason said fundraising would be a key factor in the race, and while a strong challenge could cost $30 million, the election is still 15 months away.
"There's plenty of time," Gleason said. "This is August."
Several high-profile Republicans have already taken a pass on the race, but there's been a flurry of trial balloons, including wealthy businessmen Steve Welch and Tim Burns. Marc Scaringi, a former Santorum aide, is already running but is seen as a long shot.
Gleason said that early on, some strong potential Casey challengers balked after considering Obama's 10-point win against John McCain in Pennsylvania in 2008 and Casey's even wider margin two years earlier in toppling former Sen. Rick Santorum.
"But now as Obama's polls get worse and worse, more and more people are looking at this race," Gleason said. "As the months tick by and the days tick by and the economy continues to worsen, all of a sudden this looks like maybe a better opportunity for people who maybe told me eight months ago they were not interested."
Casey has been a strong Obama ally, supporting much of the president's agenda, including the stimulus package and the health care overhaul. Gleason said hammering away at Obama's economic policies is a key to beating Casey.
"Casey will live or die based on what Barack Obama does," said Gleason. "If Obama loses, he's toast. If Obama wins, he certainly has a better chance of being elected."
Casey said he's heard those theories, but doesn't buy it as far as Pennsylvania is concerned.
"I don't think people do relationship voting, or voting based on a ticket," he said.
Christopher Nicholas, a veteran GOP political consultant, said Casey will face a tougher political environment than in 2006, when voter discontent with an unpopular Republican president fueled a Democratic wave. Casey will be on the flip side next year, Nicholas said.
Former Democratic congressman Sestak said he's spent a lot of time this year making thank-you calls to supporters, and he's found a lot of voters who are turned off by both parties and the inability of Congress to fix the economy.
"There's a great unease out there," Sestak said. "This electorate has lost its faith. There's a strong feeling that no one, in both parties, is listening to them or engaging them."
Sestak said he expects a volatile 2012 election, and - faced with a well-funded, high-profile challenger - Casey could face a tough fight.
An Aug. 2 Quinnipiac University poll indicated that 48 percent of Pennsylvania voters approved of the job Casey has been doing. Obama's approval rating was 43 percent, down 5 points from a June 15 survey. When an incumbent's approval rating dips below 50 percent, it is usually seen as a danger sign.
Democrats enjoy a roughly four-to-three voter registration advantage over Republicans in the state. They expect that having Obama on the ballot next year will likely spur stronger Democratic turnout than in last fall's midterms, giving them a boost across the ticket.
Casey's family name is seen by Democrats as another asset, since his father was a two-term governor.
"The Casey brand is pretty well-established," said J.J. Balaban, a Philadelphia-based Democratic consultant. "That gives Casey some distance from the taint of Washington. That family brand of moderation and independence has stuck with the son and it's part of the reason why he's in fairly good shape now politically."
Gleason said even if 2012 is a banner election for Republicans, Pennsylvania's GOP still needs a strong candidate to unseat Casey.
"You can't ride a wave if you don't have good candidates," Gleason said.