This should be a three man race anyway.
Bush should drop out, he is getting no traction whatsoever.
Carson should drop out, he became completely irrelevant as a candidate long ago.
Kasich should drop out after South Carolina, he had one success by default, and is not likely to have many more. He is too bland. Nothing compelling about him.
Then either Cruz or Rubio can go head to head with Trump and beat him.
I have a gut feeling Kasich is going to try to get to Ohio on March 15. He's essentially skipping South Carolina and Nevada.