Freedom of Speech
When people in prominent positions, who are likely to get publicity for what they say, criticize our president and his policies, especially regarding the war on terror, this has an effect on the war effort. Last summer and fall, when John Kerry and his supporters were going on and on about a "timetable for withdrawal" and an "exit strategy" the terrorists in Irag were emboldened. They knew that if they could just hold on for a few months, John Kerry would pull us out of Irag and they would win. Especially if they could make those few months before the election as bloody as possible and help John Kerry. How many of our soldiers died as a result of the encouragement the terrorists received?
Another effect is that the standard for what is unacceptable gradually becomes eroded and lower and lower. Read this, by Powerline. This is what concerns me more and more every day.