Bush cost the GOP the election because he took away the issue of immigration by being for open borders.
Any good anti-illegal immigration voter who failed to vote for their good anti-illegal immigration representative is to blame.
To the extent that the illegals issue made a difference, it was due to the president's dereliction of leadership and lack of strong advocacy for secure borders. He could have had the House bill, even something close enough to sign out of the pusillanimous Frist senate, and he could have won with it as an issue of homeland security as well as national sovereignty. But he chose to weasel on about family values and unwanted jobs and other such drivel.
Wasn't the whole story of this pathetic election, but--Total failure on this issue. Grade F.