The "gate crashers" were allowed to enter because they had their own camera entourage and Barry and his cronies thought it would be an excellent photo-op.
Unfortunately(?) it backfired.
Anyone remember the "photo-op" of Air Force One flying low in New York?
Another embarrassing "photo-op."

He made his announcement concerning troops for Afghanistan at West Point. A strategic photo-op.
He went to try to get Chicago for the Olympics. Photo-op.
Now he will be going to speak about
global warming climate change. Yep, another photo-op.
He is acting immature and trying to bolster his own self worth;
not the best interests of this country. He must think he is in a popularity contest with the world...
Scott