Endorsements is a curse in this election, the more the establishment endorse a candidate, the more he's going to lose. Haley, Scott, Graham, Bush and super pac endorse Rubio and Bush for SC primary but Trump still won with a big margin. Besides, G.W.B has more influence in the GOP than Romney who was only a candidate by default, but his help didn't do much for Jeb in the SC primary. So I don't think Romney vote will have a big impact. And don't forget that Trump got a lot of friends in Nevada, he's more popular than Rubio in this state. Rubio's biggest handicap is that he's a nobody, he has no history to tell and no background experience, in the mind of a lot of conservative, he represent everything that is wrong with washington.