I do solemnly swear (or affirm) that I will faithfully execute the office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States.Note that not only does the constitution, from which his power flows, lay out a basic blueprint for how to "execute the office," but it also limits the power of that same office. It's true there's no mention of limits, but they are there nonetheless.
Read the last clause of that one sentence oath carefully: "preserve, protect and defend the Constitution of the United States." The current squatter in our Whitehouse has done everything in his power, with the help of a prostrate Congress to destroy that same document from which is power flows.
Violating that oath is an impeachable offense.