By Tony Romeo

HARRISBURG, Pa. (CBS) – Republican voters in Pennsylvania will be selecting a nominee to run against Democrat Bob Casey for US Senate.

Franklin and Marshall College pollster and political analyst Terry Madonna says the race for the GOP nomination for US Senate is one of the most bizarre he’s ever seen.

Two of the highest profile candidates in the race – Steve Welch and Tom Smith — have a history with the Democratic Party. Smith was a Democrat for years, while Welch left the GOP for a shorter time.

“It’s not just a question of who’s the most conservative, but who’s the least Democratic, since each has spent a considerable amount of time in the Democratic Party.”

Meanwhile, there’s much at stake for Governor Corbett and the state party, which have put their support behind Welch.

Also in the race are Sam Rohrer, the conservative who challenged Corbett unsuccessfully for governor, Marc Scaringi and David Christian.