Apparently the Chilean security goons and the SS had a disagreement this afternoon about the security protocols for the dinner. The SS demanded that the President's personal detail accompany him through the entry, and the Chileans resisted. A Washington Times Secret Service source said "I knew this would happen" or some such thing.
Look, if the Chileans wanted to off the Prez they could have done it as he was walking up the red carpet. There were 50 of their security folks in the immediate area.
This was a turf battle between the Chilean security apparatus and the American security apparatus. I noticed from the video of the event that none of the other APEC attendees came in with their own security, so what part that played in the equation is yours to discern.
FWIW, I don't think it was any attempt at the President's life, because they had ample opportunity to do it if they wished before the altercation.
The Secret Service put themselves into harm's way for the President as necessary and as often as required. That is what they signed up for.
Most Americans and all foreign governments are aware of this. It's been going on for over a hundred years.