Candidate Steve Welch, a Chester County venture capitalist, has been on the offensive against rival Tom Smith of Western Pennsylvania, a former coal-mine owner who was a Democrat for decades and switched parties last year before starting his Senate campaign.
Smith was a Democratic supervisor of Plumcreek Township in Armstrong County from 1974 to 1981. As recently as 2010, he was elected as a Democratic committeeman from his home area. And records show he donated $2,400 in 2010 to a Democratic candidate for Congress from the Pittsburgh area.
All of which is fodder for Welch's forces. They have started a website that depicts Smith as thinking to himself, "I hope no one finds out that I was a registered Democrat for 42 years."
But the Welch onslaught may stem partly from the adage that the best defense is a good offense: He, too, used to be a Democrat.
Welch was registered that way from the fall of 2005 to February 2009. He said he voted for Barack Obama over Hillary Rodham Clinton in the 2008 Democratic primary (but voted for Republican John McCain in that fall's general election).
Welch also donated $300 in 2006 to Democratic congressional candidate Joe Sestak of Delaware County, who that year unseated longtime GOP powerhouse Curt Weldon.
Sestak, in an e-mail to The Inquirer last week, recalled that Welch had hosted an event for him in 2006 at his home, then in Phoenixville.
"While I did not know Steve Welch well, he contacted the campaign near the end of our race for Congress in 2006," Sestak said. "He offered to host a breakfast gathering at his home with associates of his, with the expectation of raising funds."
Welch has called the Sestak breakfast event "a meet-and-greet," never intended to be a fund-raiser. Both Smith and Welch have said the other candidate is misrepresenting, or at least misreading, his past.
Smith, who is the founder of a tea party group, argues that he's always been a conservative regardless of party affiliation. He says he has given more than $250,000 to Republican candidates over the years, and thousands more to conservative causes.
He introduced a television ad last week that aims to reshape the argument in these terms: "In the Republican race for the U.S. Senate, who is the true conservative?"
Welch - whose conservative credentials are vouched for by Gov. Corbett and the Republican State Committee - has said he dallied with Democrats only out of disgust with then-President George W. Bush.
He said Bush turned out to be a profligate president, running up the national debt and deficits.
The RINO issue - Republican in name only - has all but dominated a primary contest that, with nine days to go, appears far removed from many voters' minds.
'A vacuum there'
While the Democratic incumbent, Sen. Bob Casey, enjoys wide name recognition, polls suggest most Republicans still don't know about Welch or Smith, or the other candidates vying for the GOP nomination: former State Rep. Sam Rohrer of Berks County, who was a 2010 gubernatorial candidate; decorated Vietnam veteran David Christian of Bucks County, who in the '80s was a GOP candidate for Congress, and lawyer Marc A. Scaringi, of Cumberland County, near Harrisburg, who once worked for then-U.S. Rep. Rick Santorum.
John J. Kennedy, who teaches political science at West Chester University, said, "There's a vacuum there, because there really isn't a well-known candidate in the field."
Casey's only Democratic primary foe, Joseph Vodvarka of the Pittsburgh area, has been all but invisible.
The Welch-Smith squabble could provide an opportunity for Rohrer, who has moved quietly around the state for months talking to conservative groups. He was the most conservative candidate for governor in the 2010 GOP primary, and was a staunch advocate in the legislature for doing away with property taxes.
'A dicey thing'
"The fighting over Republican credentials . . . may provide Rohrer an opening," Kennedy said.
Smith took note of the Rohrer threat in the same ad that bashed Welch as a liberal. He reminded GOP voters of Rohrer's Achilles' heel: his 2005 vote to raise legislative salaries, including his own.
Independent analysts said last week that voters almost always see loyalty to one's party - and its orthodoxy - as a virtue. But it could be especially important in the current partisan climate.
"Republican primary voters tend to be more loyal to their party than Democrats are to theirs," said Stephen K. Medvic, chairman of the government studies department at Franklin and Marshall College. "It is a dicey thing to have your Republican credentials questioned in the primary."
Medvic said Welch could be somewhat inoculated by the fact that Corbett and other party leaders back him. Those endorsements, he said, can convey the message: "Look, we're comfortable with him; don't be too alarmed."
Lt. Gov. Jim Cawley, joined by other top Republicans, reemphasized support for Welch in a conference call Thursday with reporters. "Steve is our party's best chance to beat Bob Casey," State Senate President Joe Scarnati said.
Meanwhile, the debate over who's the real Republican has been egged on by the Democratic State Committee, which has researched - and loudly proclaimed - the Democratic pasts of Welch and Smith.
Medvic said the Democrats may be trying to build a flip-flopper case against Smith or Welch, should either win the primary.
"The argument may be, 'You can't trust these guys,' " he said. "Who knows where they stand politically?"
Contact Tom Infield
at 610-313-8205 or email@example.com, or follow on Twitter @tinfield.