The only conclusion you can draw from the GOP behavior is that, ultimately, they simply don't disagree with the Democrats on a lot of these issues. Yeah, they're craven cowards, unprincipled (which they invent euphemisms for, like "pragmatic," "realistic," "nuanced," or "Realpolitik") but cowardice can't explain everything.
I'm now beginning to believe that they might even be deliberately cultivating the image of cowards, just so their frustrated voters will attribute their treachery to being weak willed rather than the truth -- that they are in active agreement with the Democrats.