Johnson did not get enough votes in VA, FL, PA or OH to cause a Romney loss. It was tight, but Johnson was not a major reason for the loss. Low turnout was. Compared to 2008, 14 million stayed home. Factor in population growth and it is closer 20 million.(R needed 67 electoral votes to flip, or about 2 million votes in 4 states. If so, he wins the Pres, but looses the popular vote.)
Romney caused the loss, no one else.
the number Romney needed in four states was close to 350K not 2 million:
Florida/29 EV/Romney lost by 50K votes..
Ohio/18EV/Romney lost by 105K votes
Virginia/13EV/Romney lost by 115K votes...
Colorado/9EV/Romney lost by 115K votes (this one disturbs me)