At least 49% of Pennsyvania Republicans voted against Specter in 2004, and it only emboldened Specter to move further leftward and screw over the GOP more.
Speceter ran as a Democrat because he knew he couldn’t win a Republican primary. His poor polling shows that his party switch looked flaky and opportunistic. I don’t blame you for disliking Kirk’s record, but conservatives may have some leverage over him now.