An EO can not execute a law, and it certainly can not bypass a Constitutional right.
Building a border around federal property, like around a Post Office, is clearly handled under Executive oversight. Just happens that the wall he wants is around a big piece of federal land.
DACA was done by EO because Obama could say stop prosecuting these cases. Let them languish. If you prosecute you will be terminated from gov't service.
Climate Change stuff could be done under an EO, no issues there.

