The key to Douthat's explanation is that there are different reasons for different factions supporting Trump. It's this coalition that gives Trump his shot at winning the White House.
Douthat's explanation combines the hope of mainstream conservatives for a conventional Republican leader with the wish of the alternative right to burn it all down and start over. Each faction is betting on an outcome favorable to their view of politics. Here is Douthat's nut graph explaining what's going on:
Read the rest of Douthat's column. Spoiler alert: he doesn't believe Trump can be restrained, and he isn't personally willing to sign on to the risk of "economic or geopolitical calamity" that a Trump presidency might bring with it. So he stands outside the coalition. But maybe, just maybe, enough voters are willing to bet on one of the other outcomes to allow Trump to ride that coalition of opposite bets all the way to the White House.If Trump gets restrained by his advisers, he'll be a typical Republican, this combination would go, and if he stays true to his own essential Trumpiness, he'll be the scourge our rotten system needs.
Source: Ross Douthat.