1. The perception that immigrants are taking away jobs.
2. The plight of the working class; the loss of good-paying manufacturing jobs.
3. The feeling that, for a number of reasons from internal social decay to external threats related to terrorism, that we are no longer safe.
4. The strong resistance to Globalization.
5. Disgust with D.C. in general.
6. The huge loss of opportunity for advancement for the working and middle class.
7. Possibly a backlash against social policies of both Republicans and Democrats.
8. The feeling among conservatives in general that the Republican Party has deserted or betrayed them.
9. Among small businessmen, the explosion of regulation and the cost of compliance.
That's off the top of my head. I'm not saying I believe Trump can address any of this; I'm saying that he gives people a focus point for rebellion.
Well let's take these one by one:
1. Immigrants are NOT taking away jobs, this is a false perception. Therefore it's not a legitimate concern.
2. The loss of good paying manufacturing jobs is a legitimate concern. But it's not one that can be addressed by the sort of instant and simplistic solutions that Trump is calling for. And so long as the people who support Trump insist on such solutions which most economists tell us would be damaging to us, why should we pay attention to them?
3. These are anecdotal fears based on news stories. Statistically, we're safer than we've ever been. Should we address anecdotal fears through suppressive laws, the way we did during World War II when we interned Japanese Americans? I think as a nation we have moved beyond that. I don't know how to address irrational fear beyond repeating that fear itself is the only thing we have to fear.
4. I don't think most Trump supporters truly understand what globalization means. This is a paranoid fear, and not legitimate.
5. Most Americans have felt disgust with Washington for 100 years or longer. So what?
6. This goes back to #1. Legitimate concern, but requires long term and deeply thought out solutions of the kind we're not getting from either party (and certainly not from Trump!)
7. You'll have to be more specific here.
8. I think this is a huge concern among conservatives, and it's completely illegitimate. Consider their two main complaints: they wanted the Republicans in Congress to shut down the government over Obamacare, and to refuse to raise the debt ceiling. Because the GOP leadership wisely chose to avoid these disastrous moves, they were considered traitors and we basically have Donald Trump as a result. This particular disconnect is largely due to the irrational demands of talk radio hosts like Rush Limbaugh and Mark Levin who have no connection with the real world.
9. This is the most legitimate concern. It's why we need a rational conservative counter view to the Democrats, who will never address this issue.