In answer to your question, I think it's important to understand that the safe third country agreement also has exemptions. You can come to a legitimate port of entry, and under one of several exemptions, make your claim there, and your claim will be heard. When I say will be heard, I should qualify that. A decision will be made on whether or not the claim is eligible. If it is, eventually it will be heard by the board.
In answer to the question how would we turn people back and send them to the States, I think it would fly in the face of all our international obligations, and the values we've put forward. Might is right. If we wanted to implement something like that, it would have to be done operationally hand and glove with our U.S. counterparts, but it would be, on the face of it, a strong departure from an established rule.