I think you are right that Trump never expected, at the outset, to get this far.
Similarly, in that respect, I think neither Obama nor his handlers expected him to beat Hillary in 2008; they were preparing for a future run, maybe 8 years later.
And that, of course, is the primary reason we have had such an unprepared, bumbling incompetent in the White House for the past 8 years. But who knows? Hillary might have been just as bad, if her performance as Sec'y of State is any indication.