When Sen. Arlen Specter of Pennsylvania suddenly became a Democrat in April, it seemed he had virtually ensured his re-election to a sixth term in 2010.
The veteran senator had the backing of President Obama, top state Democratic leaders such as Gov. Edward G. Rendell and Sen. Bob Casey and was all but assured of the Democratic nomination in a state that has been trending heavily Democratic in recent elections.
However, a new set of obstacles stands in the way of the senator, who switched parties in the face of polls showing he could not win the Republican Party's renomination.
Rep. Joe Sestak, a relatively little-known two-term House Democrat who senses that much of his party's base is uncomfortable with Mr. Specter, confirmed last week, "I am going to get into the race against Arlen Specter." Recent polling shows Democrats cooling toward Mr. Specter's candidacy amid doubts raised by his long history as a Republican warrior who took positions and cast votes sharply at odds with those of his new party.
A Franklin & Marshall College Poll (formerly the Keystone Poll) of Pennsylvania voters reported last week that 28 percent said he deserves re-election, down from 40 percent in March. While it showed he was holding on to 43 percent of Democratic voters, just 24 percent of independents and 11 percent of Republicans questioned by the pollsters supported keeping him in office.
"In every poll we did asking does he deserve to be re-elected, he seems stuck at about 30 percent support. In other words, he has not been able to establish dominance," said G. Terry Madonna, director of the poll, conducted by Franklin & Marshall's Center for Opinion Research.
Mr. Madonna cited several possible factors for the findings.
"One, we've got a fluid Senate race. You have a situation where a large number of Republicans have deserted Specter after he left the party. Two, Democrats have not bought into his candidacy, and independents are concerned about his party switch as well, that it was done for political survival reasons," Mr. Madonna said.
Mr. Sestak is on a three-week tour of the state, reminding Pennsylvania Democrats of the former Republican's votes for President George W. Bush's agenda — from tax cuts to the Patriot Act to his Supreme Court nominees.
Whether Mr. Sestak will be able to raise the money needed to make himself better known and be competitive in a statewide primary race remains to be seen. He has been relatively successful in raising significant sums for his congressional races.
Mr. Specter, on the other hand, seems assured of significant financial support with Mr. Obama, Mr. Rendell and much of the Democratic establishment behind him. He also is running well ahead of his likely conservative Republican opponent, former Rep. Pat Toomey, by 11 percentage points in a recent Rasmussen Reports poll.
Democratic campaign strategists, however, are skeptical of Mr. Specter's ability to win large numbers of rank-and-file Democrats in a party primary, especially given his record of voting with the Bush administration more than 60 percent of the time.
"Specter could very well have a tough fight on his hands. He's facing an opponent who can raise a lot of money who is a relentless campaigner. The fact remains that he was a Republican who cast a lot of bad votes," said a Democratic campaign adviser who did not wish to be identified.
"There are Democrats in Pennsylvania who feel Specter can't be trusted, and they question whether he will do the right thing if he is re-elected," the adviser said.
John Brabender, a veteran Republican campaign adviser in Pennsylvania politics, said he thinks "Specter miscalculated. He thought Democrats would be out in the streets cheering, and frankly, they are not."
"Specter has two problems. He has to win the Democratic primary and then he's got to defeat Pat Toomey. I think a number of these polls are accurate. There is a real dog fight going on in Pennsylvania. The Pennsylvania Senate race will be on everybody's target list before this is over," Mr. Brabender said.
"Sestak will absolutely do some damage. He doesn't have to match Arlen dollar for dollar, but he has to get his message out, and there's no doubt that moveon.org and other liberal groups will help him raise what he needs," he added.
Mr. Brabender also said that Mr. Toomey, who came close to defeating Mr. Specter in a party primary in the senator's last election, has been getting support from "more of the big donor types who helped Arlen in 2004, and they are now helping Toomey raise money."
Independent analysts, however, say that while Mr. Specter will run into some trouble over his Republican voting record, he could be helped by his Democratic primary challenger.
"Yes, Specter has some problems, but he can overcome them. In fact, Sestak ends up making Specter a better Democrat," said Jennifer E. Duffy, senior elections analyst at the Cook Political Report.
"Having a primary opponent will make Specter more conscious of his [Senate] votes. The result is that Specter likely becomes a more reliable Democrat vote. Sestak essentially keeps Specter in the Democratic corral," Ms. Duffy said.
Mr. Specter has survived close Senate races before by appealing across party lines and winning labor union support as well. However, Pennsylvania has turned decidedly more Democratic in recent elections, and observers say he faces a much tougher situation in this election cycle.
"He ends up in a situation where Obama, Rendell and Casey have embraced him, but there are still lots of voters who have not accepted Specter's conversion. I think the race will be more competitive than people might otherwise think," Mr. Madonna said.