From what I know about the USA's system it is binary - while you technically have more than two candidates it'll be one of the major two (republican or democrat) who'll win. So not voting or voting for a third party (which has no chance of getting elected(?)) means you don't change anything, and if Trump wins without those blocks then that means you're indirectly supporting him, simply by not opposing him with the only realistic option you have.

Please correct me if I'm wrong