In 2007 Coleman voted to stop the amnesty, a bill that would have ended the US as we know it. That's better than a bunch of other so-called GOP members did. He's a also a vote that the party needs to caucus with to stop democrat idiocy. At this point he needs all the support he can get since he's obviously being sandbagged, which even you acknowledge.
Indeed, he did, just about two days after he voted to favor the amnesty. If you recall, there were two votes that week. Like all great politicians, Coleman likes to be sure he is firmly entrenched on both sides of most issues.
It may be that Coleman is as good as it gets in a liberal state like Minnesota. I simply think Coleman has a great deal in common with bill clinton. He won't tie his shoes without poll numbers supporting the endeavor.