The first two of these points about Donald Trump are obvious but nonetheless worth repeating, during the froth of current Trump-driven excitement. The third might have escaped your notice.
1) Donald Trump will not be the 45th president of the United States. Nor the 46th, nor any other number you might name. The chance of his winning nomination and election is exactly zero.
Why? Forget the majorities of his own party’s voters who say in some surveys that they would “never” vote for him. Instead, consider this aspect of his background:
All former incumbents had been through some sort of public service before running for the presidency. The great majority of them had been elected to something: The House, the Senate, a mayorship, a governorship, the state legislature, the vice-presidency, something and usually many things. Of the few exceptions, all had held important non-elective public positions. William Howard Taft and Herbert Hoover had been Cabinet secretaries before running for the White House; Zachary Taylor, Ulysses Grant, and of course Dwight Eisenhower had been famous military commanders.
To put it another way, the number of presidents between #1 and #44 who took office, as Trump would, with absolutely no elective, appointive, or military public experience is … zero. (The most recent major-party counterexample would be Wendell Willkie, a corporate lawyer and one-time Democrat who had never previously run for office. As Republican nominee in 1940 he took 82 electoral votes, versus 449 for FDR. The most recent third-party illustrations would be Ross Perot and Ralph Nader, neither of whom won any electoral votes in their repeated runs. All of these men had served in the military but not held public office.)