As a non-american, both side seem to be equally part of "they". H. Clinton is only the "other side" of Trump because the american politic system is de facto bipartite. Which easily answer one's wonder: "they" did not only get half the vote, "they" got all of them.

To the question "how did they got the vote to be finalist", I'm afraid I don't have a better answer that the one that's repeated and repeated so much that it's becoming a gimmick: money, media, fear and stupidity