If Romney doesn't get the nomination, his supporters will probably vote for Obama, just as they did in 2008.
I'm not sure about that. I've posted articles about exit polls for 2006, 2008 & 2010. IIRC, moderates and independents swung 2006, and independents swung 2008 & 2010. Enter 20xxexitpoll as a keyword where xx is 06, 08 or 10. Check my posts and see for yourself.
Romney supporters will vote for Obama if Romney *GETS* the nomination. For Romney supporters *ARE* full bore, progessive Obama lovers.
And why settle for second best?