Nate Silver describes Evan McMullin as...
The logic is simple: Evan is in a virtal tie with Clinton and Trump in Utah and competitive in other Western Mountain states.
Gary Johnson is competitive only in New Mexico.
New Mexico has five electoral votes. Utah alone has six.
If neither Clinton nor Trump reaches 270 electoral votes the decision will pass to the House of Representatives, where McMullin served as policy director of the Republican caucus, And the House, according to the procedures established by the Constitution, would choose between the three candidates who received the most electoral votes- most likely Clinton, Trump- and McMullin.
If you truly want to make an impact on Election Day and have the good moral judgment to reject the evil represented by Clinton and Trump, McMullin is your man.