Scott Walker and Marco Rubio will be 'bridge' candidates only if moderate Republicans don't pay attention

Rubio and Walker Competing For 'Bridge' Candidate Spot.  (Des Moines Register, 5/1/2015)
 

Sources:  Heritage Action for America, FreedomWorks

And as for Scott Walker, he's already demonstrated his appeal to very conservative voters, while antagonizing moderate Wisconsin Republican voters in the process.

Not to mention Tea Party members.