Arch is on the Potomac. It would be the tallest structure on the Potomac. DC has a height limit of 130 feet. There is nothing near that high anywhere near the Potomac. Need to go to the Washington Monument or downtown Arlington to find something that tall.
Anyway, like I said above, I don't care about this. If the FAA clears it (without Trump involvement) then so be it. The issue is that it would require a law passed by Congress. The President doesn't have the power to construct monuments on federal land, even if he tries to bypass Congress by using private funds.