WASHINGTON  — The costly Republican primary has been draining Mitt Romney’s wallet and giving President Barack Obama time to build an expansive campaign architecture with offices in 45 states and hundreds of employees.

Pres. Obama has spent more than $135 million — more than GOP challengers Romney and Rick Santorum combined — on his re-election apparatus, according to a report. That sets up his campaign to be larger and geographically more diverse than any of his opponents’ organizations.