"Foreign policy"
You have to understand the nuance of other countries to understand foreign policy let alone beat people at it. Think Marshall Plan level. Clinton has an unfavorable record, but she does understand nuance.
"Economy"
They're both total shit on economic policy. Using buzzwords doesn't improve an economy, and that's primarily how Trump wants to handle it. As the moderator of the VP debate pointed out, the debt would significantly increase under Clinton or Trump.
"Domestic issues"
Like?
"Veteran issues"
The guy who withheld a donation that was supposed to go to veterans beats people on veteran issues? What's he going to do for veterans?
"Immigration"
Ahem. There are very SIMPLE administrative strategies to improve border security. Politicians don't do it because talking about doing it is easy votes every 2, 4, or 6 years. It has been since at least 2008, the earliest election of my living memory. This involves utilization of modern technologies for considerably better monitoring, and it'd be even simpler if we worked an immigration deal out with Mexico (which isn't actually terribly difficult). Trump is another such person who likes to talk shit on this issue without giving any good or realistic idea about it. Build a wall? It would be incredibly costly to build, let alone maintain, especially considering how massive the US-Mexico border is. There are also a number of administrative questions about jurisdiction, as well as still needing to have people watch it the entire time. They'd also have to clear out the tunnels that exist beneath the border for any border security plan to be worth shit. Make Mexico pay for it? This idea is laughable as hell. The two parties that have a chance at presidency in that country have renounced the idea and said it'd never happen. And the next largest party, besides being irrelevant, called for Trump to be criminally investigated, just as a sign of their lack of support for him. The current president has said not only won't they pay it, but that the wall would inherently be a failure, thus citing an outright denouncement of the policy, and considering how unpopular he already is, it's safe to say he'll stick to that. But, if by some miracle, Mexico did pay for the wall, their economy would crash so hard so fast, you know where they'd go? Here. Over the wall, thus making it an even more colossal failure.
"Health care"
His idea rips off cookie cutter ideas that don't increase helping people in need of healthcare. His plan is minimalist at best.