He's dishonest, brutal and dangerous. He's not stupid. The debate performance was calculated and successful.
What appears self-destructive and senseless becomes perfectly understandable, if you share his political analysis. The campaign was drawing to a close. The poll numbers, already bad, were in collapse and the GropeTapes will only make them worse. The path to victory was gone.
So he gave up on the election. He quit. No sincere apology, no contrition, no reach to suburban woman, no nod to undecided voters. Instead a bullying stalker, a promise to jail Hillary, support for Russian-style leadership, promoting himself as the irreplaceable strongman who would bring Captain Khan back to life and more.
What puzzles the pundits makes sense if they're intended for other purposes. He's turned to Plan B. First, he's positioning to capture the remnants of the Republican Party as a vehicle for himself and his Alt-Right henchmen. Second, he's struggling to restore his brand, for his own business purposes.
The fight for the Republican Party will feature the Establishment led by Jeb and Romney, the reactionary ideologues led by Cruz and Ryan, and the the angry populists led by you-know-who. The populists have the edge, but only if they keep control of the masses of Trump voters. To do that, throw the base red meat and plenty of it. No compromise, no backing down.
There's more than Trump behind this. The nationalist Alt-RIght folks see Trump as a vehicle to reshape the Republican Party and the nation's politics, the American version of the British UKIP Brexit campaign. These folks are ideologues, but not of the old liberal/conservative dichotomy. In the Alt-Right universe, the threat is globalization and the remedy strong nationalism. Trump may not share that world view, but the combination of his personal popularity and their agenda is real, in political terms.
The Trump brand has been badly damaged, commercially. His hotels and resorts, his ties and sauces are going to take hits from the GropeTapes just as they prospered from his TV shows. Some of that damage is irreparable; Some can be mitigated by mobilizing the substantial numbers of continuing supporters, even if they are a minority of the country.
It will not be easy to salvage the brand. Whatever support he enjoys politically, his days as a role model are over. Lots of people who used to be drawn to the name aren't going to want to explain their continued brand loyalty.
He is likely to win the fight for the future of the Republican Party. First, he's blessed in the ineptitude of the opposition. Romney and Bush excite nobody. Conservative ideology is unable to help average folks. More tax cuts for the wealthy are no longer the path to popularity with middle-class folks. And, as the primaries proved, there are more Trumpists than any other Republican faction.
The Paul Ryan flop sweat is a harbinger of things to come. He's caught between losing suburban, moderate Republican swing voters if he sticks with Trump, or losing core Trump voters if he jumps ship. Absent a shift in momentum, he's likely a former Speaker.
Making sense out of Trump isn't ignoring how dangerous this can be. We've had a stable politics for over two centuries, with the enormous exception of resolving the existence of slavery. A factional and fractional national politics will weaken the nation. The Democratic Party will inherit because of the chaos, but needs to re-establish its' relevancy to the lives of average Americans, or it will soon travel a similar path to that which Trump is guiding the Republicans.
Don't underestimate him. He's going to be around for years. With that in mind, he had a good debate.