"Like Steve Welch, Bob Casey voted for Barack Obama in 2008," Scaringi quipped, comparing Welch to the state's Democratic incumbent senator. The remark drew uproarious cheers from the audience of hundreds of movement conservatives.
Welch's support for Obama wasn't a new revelation, but it does highlight a problem for the Senate candidate that has dogged him from his campaign's onset. Once again Saturday, he tried to explain he switched his registration before the 2008 primary out of "protest and frustration" with the Republican Party.
"Let's be honest: We lost hundreds of thousands of votes across state because we didn't govern consistent with our principles," Welch said, adding that he had eventually voted for GOP presidential nominee John McCain.
But he admitted that the vote for Obama was a mistake.
"I strayed. And it was a mistake," he said. "If I had to do it all over again, trust me, I would have tried like everyone one of you to change the party from within.
"I do believe in redemption," he said. "And part of redemption is working to get rid of your mistakes and that's why I'm working hard to get rid of my mistakes."
But Scaringi didn't let Welch off the hook.
"Steve, you voted for Barack Obama for president in 2008 -- yes or no?" he asked.
After a long pause, Welch retorted, "I voted for John McCain."
By most measures, Welch should be the clear favorite to win the Republican nomination. He has the support of Gov. Tom Corbett, who brought with him the endorsement of the state Republican Party. His personal wealth, business background and southeast Pennsylvania residence, where most of the state's population lives, also seem to make him the party's strongest bet against the still-formidable Casey.
But his previous partisan heresy - he also had once supported ex-Democratic Rep. Joe Sestak - has muddled his chances. A straw poll taken at the conference put him a distant third among the attendees, at 19 votes, well behind grassroots conservative favorite Sam Rohrer and former coal magnate Tom Smith. More than twice as many people said they were undecided about the race than said they backed Welch.
His struggles appear to open the door for either Rohrer or Smith to win the primary, but each carries his own baggage. Smith made millions in the coal industry, but was a registered Democrat until recently. He's invested millions of dollars into his campaign so far, but has yet to separate himself from the pack despite his financial advantage.
Rohrer, a former state lawmaker for nearly two decades, was the crowd favorite Saturday and won a commanding victory in the straw poll. He also received an endorsement from former presidential candidate and grassroots favorite Herman Cain, who spoke at the Political Leadership Conference shortly before the Senate debate and delighted the audience with a stinging rebuke of the Obama administration.
But Rohrer lacks money, and managed to win only 30 percent of the GOP vote two years ago when he ran in a primary against then-Attorney General Corbett. And as Saturday's debate indicated, his sharply conservative agenda could make beating Casey a long-shot.
Asked how he would reform Social Security, Rohrer said he would remove financially disadvantaged people with disabilities off the program, a dramatic proposal that could draw severe blowback in a general election.
"That is a program Social Security was never intended to fund," Rohrer said.
Their liabilities contribute to the distinct sense, felt among the conference's attendees and a range of the state's political strategists, that the Republican Senate race is a toss-up, with either Rohrer, Smith or Welch capable of emerging victorious. With the state's primary on April 24, that could leave the candidates in a one-month scramble for the party's nomination.