I heard several analysts on Tuesday night saying that Trump was the only one who saw the wave of populism and figured out how to get on it. I think this is giving Trump way too much credit for being in the right place and time. I certainly won't say that he deserves no credit for winning the election, but let's think about the populist wave and resentment against Washington.
There is always a lot of resentment against the government. If you don't think so, you probably live in a wealthy section of a big city, because I am sure it is there and I hear it all the time. In many ways, Reagan's election was the same theme, and there have been many would-be populist candidates in the meantime. Think about Ross Perot, Pat Buchanan, Hermann Cain, Bernie Sanders...They all lacked something. One thing they lacked is that they never got a major party nomination. Perot didn't even try. If he had (and I don't know which party that would have been), I'm sure he could have won. It would have been difficult to defeat Bush for the Republican nomination in 1992, but he might have had a chance in the crowded Democratic field. (I have no idea if he would have gotten any support for his policies, but he does seem to have crossed party lines with his support.)
The other candidates tried but failed. Maybe the presumptive candidate was too powerful to lose to an outsider. Sanders had a hard battle against Hillary Clinton, and came close to winning -- may have won, had it not been for superdelegates, if I understand correctly. In a different year, such as 1992 or 2004, he might have gotten the nomination. Other candidates may have been less appealling for other reasons. Cain gathered a certain amount of support in 2012, but got derailed by accusations of sexual assault. Maybe he wouldn't have won anyway. Buchanan was the closest to Trump in one way: he was willing to say what he thought, no matter how many people he offended. But he wasn't a millionaire who had been in the public spotlight for 30+ years. That is a powerful advantage which none of the other would-be populists have had. (Perot was plenty rich, but he was not in the public eye nearly as much as Trump has been, for the amount of time he has been.)
So Trump came along at the right time, when the Republican field was open, no obvious candidate having a lot of support right away. This would not have worked so well in 2012; he might have won the nomination, but it would have been much more difficult against Romney. He might have won in 2008, but the Republicans were at such a disadvantage in that election that he would have had little chance of winning the election. In 2004, he would have stood no chance against an incumbent president. Looking back a little further, there was obviously a large populist element in the 1992 election, where Perot got nearly 20%. But Trump would not have won the nomination against a sitting president. In 1996, Perot was a much weaker candidate and still won 8% of the vote. Trump would have stood a good chance for the Republican nomination that year, as hardly anyone was excited about Bob Dole. However, Clinton had the advantage of incumbency, and sitting presidents have lost re-election bids only 5 times since 1900, most of them under extraordinary circumstances (strong third-party runs in 1912 and 1992; the Great Depression in 1932; Gerald Ford had never run on a national ticket prior to becoming president and running in 1976). (Comparatively, 13 sitting presidents did win re-election, mostly by large margins, including some of the largest in history -- 1936, 1964, and 1984 -- and several times when they appeared to have little chance, notably 1940, 1948, and 2004.) It would certainly not have been as favourable a chance for a populist Republican as it would have been this year.