Krugman’s blunt approach has powerful attractions. For one thing, it delights his liberal readers, and may inspire some of them to advocate for better policy. For another, his willingness to ascribe motive may reveal the real drivers of political struggles. In one of this book’s punchy and persuasive sections, he goes after the media’s cowardly tendency to give both sides of a debate equal treatment, even when one side is clearly lying. At his best, he is the lucid antidote to this sort of false equivalence. But the Krugmanite approach also has drawbacks. By branding Republicans as “bad people,” he reduces the chances of swaying them. By sweeping all Republicans into the same basket—often without specifying whether he means party leaders or the rank and file—Krugman may obscure more of reality than he manages to expose.

His answer to these objections is characteristically forthright. The way he sees things, sweeping “Republicans,” the “right,” or sometimes “conservatives” into one basket isn’t a mistake, because he believes that nearly all Republicans belong in there. Insulting large categories of opponents has no cost; all are more or less dishonest, in hock to special interests, and therefore impossible to influence by means of reasoned argument. “If you’re having a real, good-faith debate, impugning the other side’s motives is a bad thing,” Krugman explains at one point. “If you’re debating bad-faith opponents, acknowledging their motives is just a matter of being honest about what’s going on.” By ignoring evidence and lying, Republicans are signaling that they cannot be reasoned with. In Krugman’s summation,“the mendacity is the message.”

When you stop and think about this line of argument, you begin to get a handle on why Krugman sounds so furious. For the past two decades, he has poured his prolific talents into a torrent of Times commentary, yet he doubts whether his writings can bring people around. If a large chunk of the 21st-century Republican Party is guilty of disparaging the truth, the flip side is that Krugman himself has lost confidence in the efficacy of the truth, at least in forging policy consensus. This is a dispiriting conclusion, especially for a truth-seeking professor. The more important question is whether it is justified. Are Republicans really so undifferentiated? Will none of them ever listen to a Krugman-type message, perhaps cleansed of its bile?

Go back to the example of climate change—a topic chosen, remember, because it fits relatively easily into Krugman’s Manichaean worldview. Contrary to Krugman’s assumption, not all Republicans have the same outlook. President Trump has mocked climate science, but Republican senators such as Lamar Alexander and Lisa Murkowski are at least willing to acknowledge global warming and to call for extra research into renewable energy sources. Senator Lindsey Graham, usually an abject Trump defender, recently urged the president “to look at the science, admit that climate change is real, and come up with solutions.” In April, Representative Matt Gaetz of Florida, another Trumpy Republican, tweeted, “I didn’t come to Congress to argue with a thermometer, and I think that more of my colleagues need to realize that the science of global warming is irrefutable.”