There are plenty of reasons to change the US Constitution, but I’m wondering specifically about the current dilemma the US seems to be in re the executive seeming to have no desire to listen to the courts. The US Marshals, the law enforcement arm of the judiciary, is ultimately under the control of the executive. What changes would need to be made to the Constitution to ensure that there 1) can’t be a conflict between separate law enforcement agencies in two branches, and 2) the executive branch can never, even theoretically, have the ability to seize control of the government from the other branches?
The only change needed to prevent any of this (or Bush Jr) is language that prevents anything like the Electoral College.
The EC was a concession made to get the constitution ratified in the first place, but with a magic wand you could make that happen.