- Trump has name recognition. That goes far, alas. After all, Bush, Clinton, Bush, Clinton.... Of course, Jeb! could not parlay his name recognition into votes, but fame does have its advantages.
- Trump has more media experience than the rest of the field.
- Trump had more media attention than the rest of the field. Why? Because he is living clickbait--his "unscripted" ways meant that every day there was a new car crash to cover.
- Turnout in primaries is low with the most passionate showing up, and Trump was able to get a bigger percentage of these passionate people.
- In a time of hate of the establishment, Trump was the best positioned. Cruz did better than most since he is also an anti-establishment candidate, but, damn, people dislike him. Experience in this race meant being tainted by the establishment.
- Which speaks to this: what an incredibly weak field of candidates.
- Outbidding! In an auction for the votes of the frustrated, angry folks who want to blame others (Muslims, immigrants, women, African-Americans, Jews, etc), Trump consistently offered the most extreme stances. Having no shame can be handy that way. The rest of the field could not really take him on for his xenophobia and racism since they wanted the votes of the xenophobes and racists. This is a problem that Hillary Clinton is not going to have.
- Winner take all sucks for those who don't win. The Republican rules really favor the frontrunner. Clinton would be done with Sanders at this point if she had the same rules.
- Collective action is hard. The competitors kept coming up with cooperative efforts to confront Trump a month or three late. They could just not cooperate.
I also think HRC's experience will pay off in the debates, that the divides within the GOP are far more significant and relevant than those in the Democratic coalition, and that people will not be comfy with Trump being close to the nuclear button and all that it stands for.
But I have been wrong before ...