Not to mention assassinate at least 150 Mexican law enforcement officers. And uncounted civilians.
It is apparent that they never considered the consequences of their actions.
Mexico could charge, at the UN and International court, that this is an Act of War, and likely be sustained at the General Assembly and Court. A US veto on the Security Council would prevent UN action, but the US would be adjudged "waging aggressive warfare" and be guilty of human rights crimes and defenseless in court.