If you can imagine Donald Trump winning a Republican primary, then he can win the nomination.
If he wins the nomination, we can become President.
What would that be like?
Trump wouldn't be able to do much of anything without the assent of Congress. But that Congress would likely be tilted towards him, given the composition of the electorate that would have to turn out in order to elect him.
Also, he's rich. He is less likely to feel the tug of special interest politics than just about anyone in the race. He will always be more beholden to his image, and to his core message, than he'd be to any donor.
And that's why, if he's elected, he would probably slow down and moderate. The crucible of a presidential campaign changes candidates. It is humbling. It is hard. It is exhausting. Trump might seem like his expensive suit has a coating of Teflon on it now, but that's simply because his opponents haven't yet discovered what his political vulnerability is. It's there, because he's human.