Senator Brownback has just ensured that he will have no chance of being nominated for President. No Republican will get the nomination unless they support President Bush and our troops for victory. Brownback is being foolish, and it is a shame.
I think you vastly overestimate the popularity of the war at this point, even among Republicans. It's still popular on Freerepublic. But if it were popular outside of Freerepublic, the GOP would still be in charge of Congress. I have too many Republican relatives who are starting to sound like Brownback to share your optimism.