I think Sevenpin nailed it. At least for me, I'll admit I don't think Trump will be a good President. What I like about him is that everyone else in the media (sevenpin left them out, they play a pretty big role in the fed up American too, IMO) and in DC hate him. He is the Al Czervik in a system of Judge Smails. The media and the GOP (and to lesser extent the DNC) have all teamed up and are trying so hard to keep him out of Bushwood. You can't help but pull for him, because we all know it's not US they are looking out for here.
And like sevenpin says, they have brought it on themselves. Approval ratings and polls have been horrendous for years, but they change nothing. Year after year it's the same old issues, the same lame promises that are never kept, the same the same the same. Meanwhile, avg. Americans keep losing jobs to foreign sweatshops. Then they get to read the sob stories about those poor Wall Street execs who will "only" get a mere pittance of a bonus this year. I saw one article bemoan that some will get less than $150,000, which is roughly 3x or more the median income of most American families. It's $150k more than those who are unemployed because the plant shut down and moved to Mexico.
Healthcare costs keep going up, but nobody will post prices of what doctor visits, procedures, or tests cost. Patients are forced to buy health insurance, but are at the mercy of backroom deals that decide which doctors they can see, rather than requiring ALL doctors/hospitals to accept ALL insurance and honor the same deductibles and pricing for all. Funny, Congress will puff up their chests and investigate price gouging when gas is $5 a gallon, but they won't do the same for the health care industry.
There's plenty of other issues (I haven't even touched on our crumbling infrastructure, illegal immigration, skyrocketing education costs, or Social Security/Retirement concerns) and I think people are simply sick of corporations influencing policy, and are waking up to the fact that politicians do not represent American citizens... they represent corporations, maybe not even American ones, (who buy policy with large campaign contributions and speaking fees). "The People" are just there to pay for everything.
Anyhow, we know any "Party Approved" candidate will be just another shill that will sell our future for a quick buck (and Trump will too), but at least Donald pisses them off. Until people are ready to pick up arms and full on revolt, pissing off the establishment is the only way to get the point across that we're fed up and pissed about being marginalized and misrepresented.
The hope is they will get the point and better serve America by balancing the needs of the many with the needs of the wealthy. A healthy system is reciprocal. Right now it is not.