How will the Trump presidency end?

[Anomalocaris]

Resignation. Once it sinks in that a president can't do whatever the hell he wants whenever the hell he wants, Trump will rage quit like the angry child he's always been.  Two years, tops.

Boru

Dream on, he will not resign, and he would not admit to defeat in the next presidential election.  As he is frustrated he would become increasingly pathetic but also increasing strident.   The republicans will periodically make a show of opposing his more idiotic and traitorous behaviors, but that is purely for show.  The real purpose of the Republican Party will be to use trump as a cover to fortify the extreme right wing social and religious conservative position.

The real constitutional crisis and the wound that would lead to the slow death of the American system  would come when trump tries to take a torch to the American presidential election process in 2020 when he is again down in the polls, or worse, after he had lost the election.  

Trump won't succeed, and would be expelled and permanently disgraced, and his name will live in infamy and his line utterly damned.   But having set the precedent, every subsequent Republican right wing candidate will consider this or similar act a viable tool in an electoral emergency, until eventually another will try the same thing after better preparing the conservative military and policy elite then trump and his vulgarian outsiders could, and will overthrow the republic in the name of defending it.