Your point concedes that there are/were many causes for the "destruction" of the Republican party, while you specifically fingered Bush's approach on spending, the war, and immigration.
Assuming for the sake of argument that you are correct, can you really say it was Bush's approach to these issues, and not the inherent divergent approaches to these issues within the party's ranks, that caused the division?
IOW, is there a politician on the face of the earth, using political tools, that, under all the circumstances, could have reconciled all the inherent divergent views on these issues within the party to the even more wildly divergent political reality outside the party?
If not, then was it the politician who "destroyed" the party or was it political reality?
I do agree that Bush could have taken a more conservative approach in several areas. However, I do not agree that it is correct to analyze the effect of an administration on its party in "pieces."
To do so, just plays into and gives legitimacy to the "single issue" (or, in effect, multiple "single/handful of issues") mindset.
An administration can never be successful when measured against the multitude of "single issues" inherent in a party.
What will destroy the Republican party is it becoming more and more like the Democrat party: that is, more and more a loose coalition of multiple "single/handful of issues" subgroups who are unwilling to measure the party's success in terms of "net gain" rather than on a zero-sum basis viz-a-vis a handful of issues.
When subgroups form around their handful of issues, and then measure the party on a zero-sum basis---e.g., the party didn't do what I thought was appropriate on immigration [fill-in-the-blank with an issue], therefore the party accomplished NOTHING across the board---NO party can endure and NO politician can cause it to endure.
The flaw in GWB is that he has left a “base” that practically no longer exists and is totally demoralized. And he has procured no Democrat support to replace that base, as he apparently sought to do.
And let's not forget that this axiom (because it's true), must be added into the mix: "Hell hath no fury like a woman scorned".
Noonan has _felt scorned by GWB_ for a long time. She has never forgiven him for not choosing her as his speech writer, and the grudge she's been carrying is evident in many of her columns. She can't hide it.