I think the frame work that a sitting president can't be tried until impeached is sound. If not you would have a never ending load of cases against every president for any conceivable slight. That said once they become a normal citizen again impeachment would no longer be necessary, and cases should go straight to court.
Unless it specifically says it's void at termination it would still be enforceable. They also spread the gambit from don't take clients to you can't work within so many miles, or for so many months/years.
If the company fires that sales person then they're out on their a$$ and the non compete still applies, so they have to start over. How is it fair that a company can chain a person like that, but it doesn't work the other way around? Again, NCs are terrible for people and only good for businesses.
That right there is why they're so awful. A company should value and work to keep it's employees and customers. If they can't do that that's their problem, not a legal one.
Non competes are stupid and just hurt common folk. You still can't steal IP, trade secrets, or patented things when you leave, and the work you do on company property is still theirs.