Well, despite what NASA may or may not have been telling Rep. Rohrabacher about its internal evaluations regarding the merits of alternate architectures that did not use the SLS (and those that incorporated fuel depots), the agency had actually been rather busy studying those very topics.
And guess what: the conclusions that NASA arrived at during these studies are in direct contrast to what the agency had been telling Congress, the media, and anyone else who would listen.
This presentation "Propellant Depot Requirements Study - Status Report - HAT Technical Interchange Meeting - July 21, 2011" is a distilled version of a study buried deep inside of NASA. The study compared and contrasted an SLS/SEP architecture with one based on propellant depots for human lunar and asteroid missions. Not only was the fuel depot mission architecture shown to be less expensive, fitting within expected budgets, it also gets humans beyond low Earth orbit a decade before the SLS architecture could.
Moreover, supposed constraints on the availability of commercial launch alternatives often mentioned by SLS proponents, was debunked. In addition, clear integration and performance advantages to the use of commercial launchers Vs SLS was repeatedly touted as being desirable: "breaking costs into smaller, less-monolithic amounts allows great flexibility in meeting smaller and changing budget profiles."