To win the presidency, the republican candidate must first recognize and defeat the true opponent, the biased press. Only Trump demonstrates the understanding, strength, public presence, and charisma without apology to accomplish this. Though Cruz certainly has the conservative credentials, he really has little chance to win a general election. The press will obliterate him once he is targeted. He is better suited as a cabinet spot or Supreme Court justice. Also, easy to say that none of the others have the personality or leadership skills to ever win the presidency.
They're going to have to do better than they have so far. I don't think they have the influence they've enjoyed in the past. People are getting pretty fed up with them.