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I think it shapes you quite a bit. But I think Donald Trump would still have become the Donald Trump we know today. Rather than bring out his worst qualities, the attention he's recieved has given them more strength and an environment to flourish in; a better (but not bigger) peice of real estate in his personality. I don't think any amount of him being nurtured in a way that enhanced his more positive qualities would have changed his jerky nature. Internal forces could have led him to become a different person, but I don't think external forces (other people) had much of a chance of having a strong enough effect or influence to change these dominant characteristics about him.
These nature vs nurture sort of questions are so fiddly. We can speculate and theorize all we want, but no one, not even psychiatrists (though I suppose they have a better chance) can really know how much of who we are is predetermined.