In the eyes of supporters of either major party, a vote for a third party is a vote for the other major party. It may not have always been this way, but it has for as long as I've been an engaged voter (~20 years).

It depends on who the third party is.

More from Republicans: Theodore Roosevelt, probably George Wallace and Ross Perot

More from Democrats: Henry Wallace, Strom Thurmond, Ralph Nader

Who knows: John Anderson.

I think that Roosevelt, Perot, and Nader all had strong effects, I don't think that Thurmond, either Wallace, or Anderson changed the outcome.

When anyone says that to me, I respond with, "No, because otherwise I would vote for Hillary." That both angers and confuses them, which delights me.

Alternately, to people who consider it the same as voting for Hillary, I blithely say, "No, because otherwise I would vote for Trump." Same lovely effect.