Its a coup. Whether its a coup or not isn't the real problem for the US. The problem is that if they declare the move as a coup they would have to cease all military aid which in turn leaves the Egyptian-Israeli peace treaty in tatters allowing the Egyptian armed forces to fully re-militarize the Sinai as it sees fit and therefore threatening Israels security. Cancellation of aid may also result in retaliation by either the Egyptian government or the military e.g freight ships flying the USA flag may be refused access from the Red Sea to the Mediterranean leading to a hike in global oil prices and slowing the movement of American warships from one area of the world to another. The movement of American military cargo aircraft through Egyptian air space to the Gulf or anywhere else may also be stopped. The American military industry will also lose one of its most valuable customers. Basically for the 1.5B in US dollars (that doesnt even account to 25% of the Egyptian armed forces budget) they bribe Egypt with they get their interests taken care of, however, if they stop it then they will lose much more than peanuts.
Well the fact of the matter is that Egypt can never remilitarize the senai nor can block the suez. U can argue all you want but your military since the signing of the peace treaty has become an zionist backed and funded army meant to control the political scene of Egypt in favour of US. 30 years of investment of US on Egyptian army didn't come cheap. The fate of egypt is sealed as a US lackey until a visionary statesmen emerges who can unite the country. Seculars/liberals shoot egypt in the foot by ousting a democratic pres. and destroying a system before its inception, a system that could have unified egypt and gave it true freedom & sovereignty.
I hate seculars but admire Gemal abdul nasser to some degree since he was a decent statesmen who made some mistakes. Similarly morsi being a human may have also made some mistakes after inheriting 60 years of dictatorial ruled Egypt and he should have searched for a miagic wand or something that could have rectify all those mistakes of past 60 years in 1 year. Pitty he didn't have a magic wand.