Do you think that Hispanic and Muslim Americans (or other Americans who care deeply about Hispanic and Muslim Americans) share the detached "fascination" with watching the train wreck and crossing their fingers over who the "significant number of people would get hurt" are? Or is it only white guys who get to be "fascinated"? I mean I say all the time that on some limited level I am in the "USA #1, and worry about everyone else later" camp... I am wondering how much that kind of sentiment extends internally

... In fairness FarmBoy is constantly warning me of exactly this... that "USA #1!" becomes "Ohio #1!" becomes "XYZ race/religion etc #1!"
So do you think white Trump supporters feel like "Hey let's crash this thing and see what happens! Who care if a few Hispanics and Muslim Americans get F'd in the process, they're not "real Americans" anyway!"
I absolutely do think this sentiment goes very deep internally. People don't tend to value other groups of people with whom they share few or no connections, especially if the group is of a lower social class or is already viewed suspiciously for whatever reason. Some people would be perfectly fine sacrificing some people they're not connected to in order to see a large-scale political change, especially if they think it would favor them.
As you mention, the USA #1 thing is one example of this much broader phenomenon in the way humans value other humans. For instance, count the number of times an American laments the ~4700 military personnel killed in Iraq and compare that to the number of times they mention the >120,000 direct deaths and >600,000 total deaths among Iraqi citizens, most of them civilians. If they're mentioned at all, the latter will just be a footnote.
But it goes far deeper. Think about speculators in food markets: if they drive the global price of wheat up by 30%, they're not going to care about the poor people worldwide who will starve as a result. Or a corporation laying off American employees and outsourcing to some low-wage country: the corporate bosses see an advantage to doing this, and so they do it, with no concern for the lives it will wreck, who are mostly working-class types anyway. Or get a
So yeah, of course many whites who don't necessarily dislike Hispanics or Muslims themselves will nonetheless think that some Hispanic or Muslim livelihoods are a reasonable trade for damaging a dysfunctional political system. If there's one negative trait about humans that I expect really is just "human nature" which will never be eliminated, it's assigning some people to ingroups and others to outgroups, and treating the outgroup people as less important.
Of all the privileges that a middle-class straight white male gets, detached fascination is the one I enjoy the most. History is always unfolding around us all the time, but as a member of the dominant group, it is relatively unlikely that I will be one of history's victims at this place and time, which gives me an extra safety blanket. It's still possible that I in particular would still feel this way if I were Hispanic or Muslim, because I'm a rather strange person, but the odds are markedly reduced because of the personal stake I would have in the outcome. I suspect that is true of many of the other people who are fascinated by this election as well.
What I use this to do is to read and watch basically every type of news and pseudo-news source with every bias I can think of, and try to put myself in the minds of everyone I read. My go-to news sources are the NYT and BBC, but, for instance, I sometimes read a site full of "scientific" racists and other alt-right types, or I'll watch Stefan Molyneaux, a libertarian/alt-right hybrid. Sometimes I watch Alex Jones, because you don't understand Trump's campaign until you've watched him - some of Trump's debate positions (e.g. the vaccines cause autism thing) are direct appeals to that group of people. I try to really understand the sorts of paranoid conspiracy theories that are common in white America, especially the New World Order, because that's just the right-wing attempt to explain the nexus of economic and political forces that have been pushing them out of work and making them feel powerless. Of course I also watch and read left-wing sources like Democracy Now and Truthdig, and I listen to speeches by Chomsky and Hedges all the time. And then sometimes I want Russian or Iranian propaganda to get their side of things, so there's always RT and (more rarely) PressTV.
Anyway, just because I'm fascinated doesn't mean that I'm not afraid as well. It's been quite obvious for a while now that pressure is rapidly building up among the lower 50-60% of the white population, who have had their economic prospects stagnate for two generations now and many of whom are worse off than their parents or even grandparents. Many have died by suicide or drug overdoses as their hopes for advancement were crushed, and even more have been stockpiling weapons and ammo. My deepest fear about this election isn't that Trump wins, it's that Hillary wins by a tiny and disputed margin like in the 2000 election. If that were to happen, we'll long for the days of the Tea Party backlash against Obama.
I'll close with a political prediction. In the next 20 years, one or both of two things will happen:
1. There will be a large increase in right-wing domestic terrorism, possibly going so far as a domestic insurgency in rural areas, especially the Appalachians, Rockies, or Deep South.
2. A demagogue will be elected president.