It's obviously difficult (and, by definition in a democracy, morally wrong) to keep Trump from winning if he has the support to do it, although time will tell if the US system is able to deliver a verdict the majority actually wants this time (in point of fact, it hasn't in the past four or five times already).
Problem is that Trump isn't really the voice the people who are supporting him need. One of the most scathing critiques of Trump I've seen yet, coming from the Harvard Republican Society, puts it best:
"... Donald Trump doesn’t have a plan to fix [the problems Americans are facing]. He has a plan to exploit them."
There can be little clearer evidence from this than by comparing two of his speeches on the system used by the Republican Party to nominate its candidate. While he was still fighting for the race, he pointed out the unfairness of the system that appeared to risk screwing him, and the people who voted for him, over:
"I end up winning Louisiana, then when everything is done, I find out I get less delegates than this guy [Ted Cruz] that got his ass kicked... give me a break" (Donald Trump, at a speech delivered in Albany)
In fact this ended up not being true -- although Trump was correct to complain, and the entire system (for Democrat and Republican parties, as well as the Presidential nomination) is fundamentally broken. Unfortunately, after he was the presumptive nominee, he came out with this:
"You've been hearing me say it's a rigged system, but now I don't say it any more because I won... it's true... you know, now I don't care! I don't care." (Trump, in a speech at Charleston, West Virginia)
I suppose on the one hand, you could credit him for being honest that he's not actually interested in fixing a broken system now that he just coincidentally happened to benefit from it, ie what every other politician does -- but on the other, isn't that Trump's biggest supposed selling point? That he's not a regular politician? But if the angry people of America want to change something, then someone who literally, and categorically, admits that he doesn't care now that he's won, what was the point?
Trump may well win. Everyone who voted for him in that case will, in the end, be the first people to regret it. Trump is his own voice, not theirs, and is interested in himself, not them.