History strongly favors incumbents.
As for the reason to be "stuck" on Arlen, just think of the GOP and RNC as good 'ol boys clubs. Politics is an insider's game. It's hard for outsiders to prevail.
National news showed ex-mayor of NYC, Guiliani, supporting Arlen.
If Arlen loses (crossing fingers), Kyl will assume chair of Senate Judiciary Committee.
So, if Pat Toomey wins the nomination, will Senator Santorum, the RNC & GOP then trow their full backing and support behind candidate Toomey?
Just as we Virginians need to replace Senator John Warner ["Country Club Republican RINO"] with someone like your Senator Rick Santorum, Pennsylvania needs another Senator like Rick Santorum...
Too bad he doesn't have brothers just like him living in both VA & PA. Now, that would be too much to hope for...