Hillary, Trump, and double effect

Although this is often cast in terms of the lesser-evil principle, we can recast the issue by invoking another principle, namely the double effect principle. In the "canonical" for (a la Catholic moral theology), you cannot use a bad means to a good end. Since I'm not Roman Catholic, I'm not bound by that caveat. So, to reformulate it a bit:

There are situations where causing harming is unavoidable regardless of what you do or refrain from doing. Either you will cause harm or you will permit someone else to cause harm, because you refuse to intervene. Given that forced option, it may be permissible to cause harm to minimize harm. 

Put another way, there are situations where an agent performs an action that has two effects: one good and one bad. Moreover, inaction on the agent's part will have a bad effect, without the compensatory good effect.

The action may still be licit provided that the intended effect desired by the agent is good while the bad effect is merely foreseen, and not intended.

An advantage of causing harm yourself, rather than leaving it to someone else to cause harm, is that you have more control over how, when, where, and/or to whom the harm is inflicted. You can be more discriminating, and thereby mitigate the degree of harm. 

That, of itself, doesn't settle the question of voting in the 2016 presidential election. But it does provide another moral framework for weighing the pros and cons, both ethical and practical.