The GOP's lack of response to the illegal immigration marches this spring severely depressed the base. This coupled with out of control speneding resulted in a 5% to 10% 'headwind' that all of the GOP candidates ran against.
Some GOP candidates who usually win by 25 points, like Trent Lott, could absorb it with no problem, but for those that faced tight races it was just too much to overcome.
Even if the base was solidly there (and I think it was not withstanding your contention), it could not overcome the perception put forth by the MSM and the Rats that the war was not being fought let alone won in a timely manner. "Cut and run", unfortunately, is what brought many independents and some Republicans to the polls.