Whether or not it was right to deny him entry, it's clearly visible that he refused officers' orders to move away, and even tried to push by them after being told he wasn't admitted. By attempting to push by the officers, he entered their space and even made contact with them, which is assault.

From what little the video shows, I don't think he should have been denied entry, but it was wrong for him to disobey officers' orders and to charge towards them.

I'm very much against the war in Iraq, and many of Bush's policies, but this type of behavior isn't the way to go about fixing things.