I thought after Iowa Cruz would be a force to be reckoned with but his campaign has really taken some hits recently with Dirty tactics and calls that he's a liar. For a guy who says he's holier than thou its not a good look. The Carson thing was really nasty, and the Rubio doctored picture was just crass.
I have no doubt Trump will win the nominee now, all these endorsements Rubio is getting is not turning into votes. He needs to really attack trump in the debates to stand a chance, however I think Trump would crush him if he tried.
On another note, as a neutral spectator who has followed the debates and all the interviews I really like John Kasich from the Republicans. He stands no chance but seems a decent guy.