here is why:
bush is a lame duck president, hes done after this. republican congressmen and senators want to get reelected in the future, so they closer you get to the next elections and they see they dont have the people support, the republican support for the war in congress will decrease to the point that bush will bend or be bent
http://www.nytimes.com/2007/04/11/us...hp&oref=slogin
WASHINGTON, April 10 ? Republican leaders across the country say they are growing increasingly anxious about their party?s chances of holding the White House, citing public dissatisfaction with President Bush, the political fallout from the war in Iraq and the problems their leading presidential candidates are having generating enthusiasm among conservative voters.
Shawn Steele, the former Republican Party chairman in California, said the candidates were being dragged down by their associations with Mr. Bush as well as with the war. He and other Republicans argued that the candidates were in a difficult position as they tried to distance themselves from a president who is having so many difficulties, while at the same time not alienating Republican base voters and donors who remain loyal to Mr. Bush and his foreign policy.