Fred Barnes has a good article in the Weekly Standard.
Two things did jump out at me. The portion about the Hispanic vote is what I'm saying here, as well. The hard line has arguably turned off Hispanics.
The second is Bush. President Bush has a personal following, largely among people who think he has done his best and like him. I cannot speak for anyone else, but when Republicans were trashing the guy who was doing a good job calling the shots, I really did not feel like sticking my neck out for them.
In essence, the conservative revolt has now alienated the Bush Republicans - people who are largely conservative, but who bristle at those who try to impose an ideological doctrine on them. I'm one of those - largely on immigration - who has found himself increasingly leaning towards the Republican Main Street Project and the Republican Leadership Council, largely because I do not really trust conservatives at this juncture to put the Global War on Terror first.
And looking at Pakistan, can there be any that issue is far more important. Some are even willing to try to blackmail the Republican party over this, or declare that I have "sold my soul" over that stuff. And that approach is repulsive enough to overcome my general agreements with most of their positions.
Conservatism is in trouble. If I can't bring myself to back them when I agree with them most of the time, how do they hope to persuade others who may have more disagreements with them than I do?