Megan McArdle points it out:
Have you noticed all the huge antiwar demonstrations in the last twelve months? Yeah, me neither. It turns out that a lot of the energy for the movement seems to have been provided by Democrats who are a lot less worried about wars conducted by Democratic presidents. Or at least who believe that advancing the Democratic agenda is much more important than trying to end the wars in Iraq and Afghanistan. This is by no means the whole movement–but it was enough that once a Democrat took office, both the numbers at the demonstrations, and the organizational capacity of the movement as a whole, dwindled away to near-nothingness.
Not only are there no protests against wars conducted by Democratic Presidents, there are no protests against a war that the Democratic President started with no pretense whatsoever of consulting Congress. Amazing, really.