The flaw in your strategy is that the GOP needs the base to win. So what if Bush's numbers go down ... he can't run for a 3rd term. You don't get people to fight for you by selling them out to the enemy. You get them to fight by energizing them. This is pouring cold water on a fire.
It isn't about Bush. It's about Senators up for re-election who don't want to step out on a limb supporting a President with low poll numbers. Why in the heck do you think the media has been pushing those poll numbers all year? They know Bush isn't up for re-election; they are looking to scare senators and representatives!