What needs to happen is, when you run for the presidency, you must vacate your senate/house seat, you aren't representing your constituents anyway at that point. The only exception would be if your term expires before the next job starts, but you may not run for both your old seat and the presidency.

The Vice Presidential selection must also vacate their seat if the term ends the following year (like Joe Biden this year, he won his seat and the vice presidency, now the Governor will select his replacement for the next 2 years).

This will fix several issues:

1) If you are running for an office you aren’t doing the job you were elected for.

2) It gives the people control of who will represent them.

3) It will prevent seat selling buy people like the Illinois Governor, since the people will be given the power to elect who they want.