I hope you can understand the incongruity in those two statements when printed together. I do understand Trump's appeal. I went from a Trump doubter to a Trump supporter when he first appeared on the scene. I later became turned off by his whining, crying, and incoherent positions. (Some of) his goals are great. Given that he often takes both sides of many issues, and your own conclusion that he will likely fail in keeping his promises, I simply cannot support him for the nomination.
I honestly can't think of a single issue that I care about that has gotten better in over 30 years. I am simply not impressed when a candidate says he'll make sure things don't get worse. Best case scenario a perfect record and in 8 years the reversal resumes.