We were 'forcing' our way in?
The US President, just like the Chinese President, travels with an entourage, of which contains a military officer who carries a briefcase that contains war authorization codes. The Chinese government knows this. So whenever the US President go, so will his Chief-of-Staff and the rest of the entourage. Everyone in the world have this understanding. But it looks like Chinese security officers who are not informed and insufficiently trained on how to deal with diplomatic situations.