I'll also say, I disagree with Brooks about irony being the domain of the left or that it has too much of a role in Trumps un-satirisiblity. It all comes down to irony-as-shield vs irony-as-communication. The rise of irony-as-shield in the 90's is probably difficult to truly tie down to the left and more towards the rise of political apathy, but the end result is it had a dulling effect on left politics. Take for example the Gen X mocking of hippies, sure the Vietnam War was bad, but *why would you care?*. It's creates this false dichotomy that's harmful to left politics; "evil" is just as bad as "lame".
This strain of irony is especially prevalent in conservative leaning comedy without needing to take into account the rise of Pepe Frog loving irony alt-righters; from South Park, to Dennis Miller to even non-political but conservative-leaning comedians like Norm MacDonald. It all existed before, because if you "cared" you'd more likely to support bigger government. Even the rise of the culture warrior comics like Legion of Skanks, who perhaps have less of a direct tie to irony alt-righters though there is a lot of cross-over, but are rooted in more tradition conservatism, traffic in irony-as-shield racism/sexism/homophobia etc less in joke craft and more in the "isn't it fucking lame to care about this" kind of way.
This is the kind irony that Trump traffics in. As you say, you're not supposed to know if he's telling the truth or not. If you agree with it, then he's telling the truth, and if you don't, then he's just joking!
Whereas Jon Stewart trafficked in irony-as-communication, which sure, probably as a 90's comic was born out of irony-as-shield style of comedy. But the difference is, when Jon Stewart is being ironic, it's still crystal clear about what he means. He's not using it as a shield, he's using it as a way to communicate. This is traditionally what satire has been rooted in; for example you know absolutely what Jonathan Swift is actually saying with A Modest Proposal and if you thought he was actually advocating baby eating then the satire would be rendered pointless. As such, I don't think there is much of an overlap between Trump's use of irony and the ineffectiveness of satire in the Trump era.
I also think Brooks' understanding of the Colbert character is misplaced. The irony of the Colbert character wasn't that Stephen Colbert the person is liberal and the things the character is saying are conservative, but because the character is saying the things conservatives say, it becomes clearer what conservatives actually mean when they say these things. And the things they meant were often the opposite of what they were actually saying (i.e. conservatives were ironic, not sincere as claimed by Brooks). See for example, the complete lack of compassion exercised under the term "compassionate conservatism", declaring "mission accomplished" when the mission had only just started etc etc. Stephen Colbert the character can *only* work in a world where conservatives are ironic, he can't work in a world where conservatives are sincere. The success of the Colbert Report (ironically, har de har har) disproves Brooks' point.
Oh man. I posted too much. Twice.