Trump or Hillary as President, who else is petrified?

[Genersis]

Things are getting difficult.
Either Rubio or Cruz needs to drop out to stop eating into each other support if they want to stop Trump.
I fear Cruz' ego is too big and the establishment pressure on Rubio too high for either to drop out, but we will see.

I doubt Trump could build a broad enough voter base to win the presidency, not without seriously minimising his controversial views that Republicans are mostly voting for him for(so it would depend on how good he is at being everything to everyone).
Either that or if the US populace finds itself in the grip of Socialist Sanders/Corrupt Clinton hysteria...which I would think somewhat unlikely...