A physical and detailed contract signed that says he will honor and protect the constitution in all decisions and not circumvent congress or the people (no pen and phone games), filed with the Supreme Court and Congress, and by determination of 2/3rds of Congress or a plurality of the Supreme Court (with some sort of accelerated review process) or 2/3rds of governors, if that contract is breached, he will voluntary step down within 30 days of the ruling.
IE, he doesn't need to be impeached to be removed, the contract is an agreement he will follow the Constitution or step down on his own.
Trust is the key factor that causes many of us not to support him. We know he can spout any words he wants but his history shows words and the truth mean little to him so it will have to be something legally binding, not just get in, act like Obama with a pen and phone, and sneer that he can't be removed unless Congress gets the balls to impeach him (and he actually crosses the 'high crime' line).
For example, if he tries to take executive action to seize the assets of anyone sending money overseas outside of legal due process 4th & 5th Amendment, that is a violation of the Constitution and if Congress, SCOTUS, or 2/3rds of the governors says it is unconstitutional, he steps down.
Even then, just like contract he makes with his vendors and contractors, I would be wary to trust him. It would have to be rock solid.
Otherwise, everything he is spouting, to me, is just Words, words, words, a tale told by an idiot, full of sound and fury, signifying nothing.
Strike that. After some contemplation, even a physical binding contract wouldn't turn me at this point because some of the issues are much bigger than Trump, it is about the overall direction of the nation to an anti-individual, pro- authoritarian, nationalistic, unconstitutional entity, and even holding one man's feet to the fire won't change that. We need a fundamental shift and I don't want to see any empowerment of the direction we have been heading. Any victory for Trump is an empowerment of some very disturbing ideology that will continue to grow and fester like a cancer.