G. Terry Madonna, a political analyst at Franklin and Marshall College, called the "stunning" development some "good news" for Democrats in what promises to be a tough election year.
"That seat was seen as a likely prospect for the Republicans to pick up," Madonna said, adding that pundits were giving Republicans a 60-40 chance of regaining control this year of the House, where they now hold 99 seats to the Democrats' 104.
"I don't think there's any doubt that if you're an incumbent, you're in trouble, and if you're an incumbent Democrat, you're in bigger trouble," Madonna said, citing low approval ratings for Gov. Rendell and President Obama.
McIlvaine Smith's GOP opponent for the House seat will be Dan Truitt, 41, an industrial-controls engineer who has never sought public office before and bills himself as an outsider.
Truitt said Friday that he was surprised by Stevens' announcement and wished him a speedy recovery.
"My interactions with him were all very positive," Truitt said.
He said that changing the name of his opponent "doesn't really change my campaign message," and that he would continue to oppose big government and higher taxes.
McIlvaine Smith attributed her change in attitude to meetings she has had for some months with a group of like-minded colleagues.
"We're calling ourselves the Empowerment Caucus, and the hope started to rise again," she said, adding that her respite from campaigning also had reenergized her.
The fact that McIlvaine Smith has been a vocal critic of the political status quo will make it tougher for Republicans to link her to it, Madonna said, but will not likely stop them from trying.
John Kennedy, a political science professor at West Chester University, agreed.
"Being critical of the lack of reform shouldn't hurt her," Kennedy said. "Everyone is fed up with Harrisburg right now - and with good reason."
Kennedy said the Democrats would have been severely handicapped if they had to scramble to replace Stevens at such a late date.
"This gives them a much better shot of holding onto the seat," he said.
McIlvaine Smith is no stranger to tough races. She won reelection in 2008 with 53.2 percent of votes cast in a closely split district, two years after winning the seat in a recount that gave Democrats control of the House.
Joseph E. "Skip" Brion, who heads the county Republican Party, offered a preview Friday of how contentious the race might become.
"Ms. Smith turned her back on taxpayers to vote with the Harrisburg politicians," he said in a statement. "She admits she isn't committed to doing the job. And now she wants taxpayers to support her? It's a slap in the face to every Chester Countian."
Contact staff writer Kathleen Brady Shea at 610-696-3815 or firstname.lastname@example.org.