The five Pennsylvania Republicans competing in the April 24 primary to run for the U.S. Senate seat now held by Democrat Bob Casey met for a debate Wednesday night at the Union League in Philadelphia.

They made it clear they're all anti-abortion, anti-tax hikes and anti-Obamacare.

But the sharpest exchanges came between two leading contenders struggling to explain their history as Democrats. Chester County businessman Steve Welch, who's been endorsed by the state Republican Party, was registered as a Democrat a few years ago. He admits voting for Barack Obama in the 2008 primary.

Tom Smith is a farmer and former coal company owner, a tea party conservative who spent most of his life as a registered Democrat.

Along with former state Rep. Sam Rohrer, they're regarded as front runners in the race. At a couple of points in the debate, Welch went after Smith, who's spent heavily on TV advertising in the race.

Here's a piece of one exchange:

Welch: "Look, both Tom and I have been registered Democrats. I was a Democrat for three years. Tom was for 45 years. The fundamental difference is, Tom was an elected Democratic official in the ‘70s, the ‘80s and as recently as 2010. And we now learn he has a history of raising taxes while he was a Democratic elected official. And, I'm sorry Tom, raising taxes on your constituents nine times, including a real estate tax of 33 percent increase, coming up with new taxes that are still haunting your constituents today, is not conservative."

Smith: "Uh, Steve, I was very, very proud of being a Plum Creek Township supervisor 35 years ago. We ran a budget. We stayed within that budget. And the population of Plum Creek Township was very, very happy with their services."

Much of the information used in the debate was unearthed by the state Democratic Party: Smith was a township supervisor from the early ‘70s through 1981, and ran for Democratic committeeman in 2010, though he soon left the party. He founded a tea party group in Indiana and Armstrong counties.

The 33 percent tax property increase Welch referred to was an increase from six to eight mills in 1975, still well below the average rate for Armstrong County.

You can hear more by playing the two audio clips above.

Along with Rohrer, Harrisburg attorney Marc Scaringi and Bucks County businessman David Christian also are in the race.