I think it's more complicated than both of you have posted, OWF.
I take a rather broad view of a politician's "base." It's generally any voter he got last time, or any likely party line voter, whichever is applicable. A "base" consists of thre votes that are a politician's to lose.
Anyone who voted for President Bush in 2000 is part of his base.
I am part of the President's base. I intend to vote for his reelection.
And I am most definitely ticked at him for his Illegal Alien Amnesty proposal, as well as his big spending. However, the Democrats are fielding a bunch of rotters, so I'll be wearing a clothespin on my nose when I vote for President Bush in November.
The point Map Kernow made about the "disaffection of many in the Republican base" because of "the problems [the President's] spending and amnesty plan are causing among people who would otherwise consider him the obvious choice in an election against a Democrat" is a perfectly valid one. There are many people like this who voted for President Bush in 2000, and are fed up with some of his policies. I know quite a few who aren't even posters on FR. Some of them won't vote for him, though I hope the President wises up and limits the damage by renouncing his Amnesty proposal.
Is it most of his base who feels that way? No, of course not. But Map Kernow did not lie in his comments at #5 (Though I think you overstated things, MK); there are members of the President's base who are less than thrilled with some of his actions, especially of late.
You may not like that, OWF, but it's a consequence of some of the ill-considered decisions President Bush has made.