People don't always seem to understand this, but here it is: Having principles means having fewer choices.
That's true even when it feels like you could do something that might prevent a bad thing from happening. If that something goes against your principles, then either you won't do it, or you don't really hold that principle.
If you think torture is intrinsically evil, or that "going after" the families of your enemies is evil, you can't vote for someone who would do those things. I mean, you can, but don't pretend that torture or murder are against your principles.
If you think abortion is intrinsically evil, you can't vote pro-"choice". I mean, you can, but don't pretend that you're pro-life if you're willing to vote for a candidate who supports the right to choose pre-natal infanticide.
Casting a vote reveals what principles you truly have. A vote for Hillary isn't just a vote for Hillary -- it's a vote that demonstrates that a candidate with her principles will get your vote. Likewise with a vote for Trump. And the political class will take note, and adjust their future platforms accordingly.
The problem isn't just the candidates (although there are massive problems with the candidates). It's us.
This idea -- that having principles leaves us with fewer choices -- extends far beyond the election. But at least for this election, its consequences are clear.