It looks like he's the only anti-war Republican, so he will get most of those votes I think. Those people have to make up at least 10% of the party I would think.
Plus, the libertarian vote and old-school conservatives, the George Wills and Pat Buchanans if not those people themselves, which is probably worth a couple points.
Keep in mind though the Republicans who are opposed to the war are more than likely moderate Republicans, who don't take part in Primaries like their conservative counterparts do.
