Trump is alone in the wilderness. He has, at best, limited support from his party, on which he is also relying for. he's relying on basic campaign funding because he's too cheap or arrogant to run himself. Much of the right-wing media and blogosphere is against him. His own campaign is in disarray and cannot respond effectively to attacks. He apparently writes his own speeches, which hurts him inasmuch as he knows nothing about most issues and is incapable of presenting a coherent argument. Frothing anger and unchecked id do apparently have their limits, happily for the republic.
he cannot rely on events like terrorist attacks to improve them; he doesn't know how to project the kind of strength middle-of-the-road voters would find persuasive. Eventually the numbers will get bad enough that Trump cannot bluster his way around them and his fellow Republicans or going to start panicking, very loud and in public. I can't see either the Republican establishment or Trump himself being content to ride this runaway train off the cliff.
I am increasingly coming to the conclusion that Trump will withdraw. Whether the party pressures him into it or Trump decides his ego can't withstand the humiliation, an excuse will be made for him exiting the race. Today I'd put the odds at one in six. As for what would happen after that, I really do have no idea.
One thing I have become convinced of: the Trump we see in these speeches and rallies is not a persona. It's who he really is. His supporters love him because, while he's completely full of shit in terms of what he intends to do as president, he's nevertheless not being fake. In fact, Trump provides an interesting paradoxical lesson in how to lie about nearly everything while still remaining authentic to who you are as a person.