first, don't forget that ross pert took nearly 19% of the popular vote even after some major stumbles and more or less giving up late in the game.
the key is not to focus on trump himself, but on the nation's yearning for change. that is key to predicting presidential election outcomes.
1988, 1996, 2000 were all pretty good times for the country, financially at least. the nation was fine with the status quo, and the party controlling the white house won the popular vote in each of those elections (gore won the popular vote even if he was robbed of the electoral vote).
but in none of those elections was a true "outsider" likely to win. 1992 was different and ross perot had a big chance but blew it, yet quite possibly did influence the outcome.
2016 is not so simple. obama has done a great job imho, and the economy is certainly much better than the one he got when he took office. but the public is not so grateful as there still isn't a sense that our economic troubles are behind us.
essentially all the candidates are pretty "establishment" except for sanders on the left and trump on the right. i think sanders is doing well because of the same phenomenon, we're not overly thrilled with the status quo and there's some appetite for something different.
right now, the republican primary is a "trump or someone else" question. sure, his inexperience will quite possibly trip him up, but then again, maybe not. perot was genuinely inexperienced not just in politics but also in mass communications. trump may be inexperienced politically, but he is a danger when it comes to mass communications.