**IIRC, he could run as a Republican without a primary challenger, which was the deciding factor in choosing his party. Maybe some PA Freeps have better info.**
He was supported by and campaigned with ... W.. who bypassed a true conservative, which is when I started counting the days before W ... was GONE.
Yeah, that was Toomey, and Bush and Santorum both ran to Arlen’s aid, but that was last election. They were able to shove Arlen over the top, but Santorum got shoved out the next round, primarily because of anger from conservatives. I’m thinking that back when Arlen first ran, he grabbed the Republican slot because there were already a couple of Dems vying for the Dem spot, so he could sit through the primaries and just run in the general. I don’t think he has any ideological ties to the Republicans. It’s just like Jack in the Box was crowded so he went to Burger King.