Even before Giuliani’s most recent incarnation, I had been spending a lot of time thinking about him for a book I’m writing about New York in the 1980s, a sort of sequel to my earlier history of the city in the 1970s. To me, the answer to the question ‘‘What happened to Rudy?’’ had come to seem obvious: Nothing. Rather, Giuliani’s latest role — as the president’s letting-it-all-hang-out, unabashedly dishonest personal lawyer and shadow secretary of state — is more like a culmination, the purest expression of Rudyism yet. What has changed is that Giuliani’s style has become the dominant mode of American — and, really, global — politics.

Personality-wise, Giuliani is a throwback to an old New York type, perhaps best embodied by William Magear Tweed, a.k.a. Boss Tweed, another swaggering, domineering figure from the city’s past. But men like Tweed were creatures of their old-fashioned political machines, while Giuliani was among the first of a new breed, a publicity-obsessed, reality-defying master of resentment politics — that is, just the kind of figure who is now ascendant across the globe in the form of strongmen, oligarchs and even populist Tories. These are not men of vision, but men of appetites. They are typically unrefined and streetwise; they practice their populism with a knowing wink, issuing fact-indifferent, emotion-based appeals to their constituents, while focusing, with impunity, on consolidating their power, satisfying their hungers and enriching themselves. The evolution of the modern media facilitated their rise, and the unregulated platforms of social media have now eliminated the final barrier to their ascension. ‘‘Without Twitter, I think we’d be lost,’’ Trump told Rush Limbaugh just this month. ‘‘We wouldn’t be able to get the truth out.’’

The real question is perhaps not ‘‘What happened to Rudy?’’ It’s ‘‘What happened to us?’’ Today, anything seems possible for those who are willing to say and do anything. Watching Giuliani wage his destructively madcap campaigns over the course of the last two years — and continue to wage them, even in the face of the president’s impeachment and his own criminal investigation — it has become impossible not to wonder if there are any limits to shamelessness at all.