This is from a recent study by Sean Kates, Jonathan M. Ladd, and Joshua A. Tucker. As they sum it up:
… while a large majority of Americans think democracy is the best form of government, nontrivial portions of Americans disagree. They believe that democracy as a form of government tends to serve the elite, and there are times when nondemocratic systems are preferable.
But perhaps even more concerning is that the young are less supportive than older Americans of democracy as a concept. They are not less satisfied with American democracy right now, nor are they less likely to think it is responsive to their needs, but they are less likely to believe that democracy is superior to other forms of government and more likely to believe that it serves the elite.”
Another study, this one by Eric Oliver and Thomas Wood, might seems to dampen this claim, but even they show that the young today are less supportive of certain democratic values than their age group was a generation ago.