And why would they consider aligning themselves with the President risky?
It will lose them votes, that's why.
And why would that be? Because the voters don't trust the President. Thus contradicting your statement that the people trust Mr. Bush. Follow the effect to the cause. Simply invoking a stereotype of politicians' behavior is insufficient.
Politicians are supposed to be responsive to the people. That's why they often pay attention to what the people think, especially when the current is especially strong and their jobs are on the line.
