Regardless, if this is a time for choosing — and one gets the sense that it is — then I’m more concerned about long-term consequences than short-term setbacks. It is much more likely (and problematic) for the GOP to damage its image for a generation, than to lose some House races in 2014.
If the bill fails, it probably also matters how it goes down. Does it fade away (less likely), or does it go down in a blaze of glory? Is it perceived that Republicans are solely to blame (highly probable), or can the blame be spread around (as with the failed gun control bill)?
These are not arguments for passing bad legislation, but I suspect opponents of immigration reform underestimate the potential consequences.