He doesn't just have a problem with the GOP base; moderates aren't supporting him either:
Mr. Romney may have calibrated his ideological pitch a bit too finely. While not having made much headway with the most conservative Republicans, moderates are also somewhat leery of him. Were Mr. Romney polling at 40 or 50 percent among moderates instead, numbers that you might intuitively expect from a candidate who is often critiqued from his right, his base of support against surging candidates like Mr. Gingrich would be more robust. But so far he has posted somewhat underwhelming numbers with this group.