Already have the 25th Amendment to the Constitution, section 4. It 'should' kick in when the office holder is shown to be crazy as a shithouse rat. Well... tested that and.. um, er... um? Still that means they already got into office, but...
Problem with testing before an elected official is allowed to assume office.
Seems at first .. maybe okay. Except what you just did was overthrow the will of the electorate. Because you hafta looket who is making the test. The following example is kinda extreme seeming, but.. basically are setting up a thing so an elected official has the new version of "Sluggish schizophrenia". The favored diagnosis for dissidents in the USSR.
So ... the actual fixit. I dunno? I mean I kinda have an idea, but... not sure all the details, or if it would ever be implemented anyway?
Basically ya gotta figure out better way to distribute power, then is just harder to break stuff.
Distributing the powers more inline with using population to select the representation.
Statutory setups that would make it harder to get 'executive authority / executive orders' wiggle room.
Methods to prevent a single political party 'locking up' the whole mess.
Some of this can be done in the USA w/o needing Amendments, but some of this is gonna need them.
Increase the size of the House, the population side, thus shifting the weighted average of the Electoral College away from geography.
Change the powers of the Senate, the 'geography' side of the weighted average, making it more of a subservient advisory body to the House.
Things like all the powers to screen executive appointments should rest on Population selected Representation, and the power to initiate bills would rest in the House only, with maybe a 3/5th or more vote in the Senate able to say "Nuhuh.. try again". Something like that is because I still don't trust .. anyone! So checks are good.
Move some more of the 'executive functions' to the House. Unsure of the details, but again.. is just adding checks.
Then ranked choice voting, most likely result would mix up the system and increase the number of parties.
And toss Citizens United verdict out on its ass....
Freedom of Speech is important, but implied in its exercise is the prospect of being punched in the face for saying stupid shit.
Corporations don't have faces to punch.