With “The Big Con: The True Story of How Washington Got Hoodwinked and Hijacked by Crackpot Economics” (Houghton Mifflin, 304 pages, $25), the New Republic’s Jonathan Chait has written a fundamentally unserious book about a critical problem in American politics, and by so doing has disserved his readers and even those who share his political point of view.

From the title alone, the canny reader will deduce that a conspiracy theory is coming, and sure enough, on page one, Mr. Chait says that, although he personally does not like conspiracy theories, in this case he feels compelled to offer one. Surely the public will understand, he suggests.

Mr. Chait’s beef is with Washington. These days, he writes, no one in the capital city seems ready to support tax increases, income redistribution, and new government programs, even though Mr. Chait asserts the American public wants and needs these things. Indeed, Mr. Chait asserts, the American public knows it needs them and wants to pay. Something must be wrong with today’s politics, Mr. Chait believes, if it fails to deliver the policies the public demands. In a better, purer time, back in his father’s day when Mr. Chait was still a very young man, enthusiasm for big government ran high and tax increases were always matter-of-factly on the table, if not outright automatic. This was, Mr. Chait believes, a halcyon age.

Mr. Chait hankers, it seems, for the economic policies of Lyndon Johnson’s Great Society, produced by a moment of unquestioned dominance for American liberalism. Then, liberals saw their views as the social consensus from which all rational policy discussions had to start. A serious book would honestly and objectively ask what went wrong since Johnson, and why. Did his policies work or not? Could it be that economic science has advanced? How could today’s liberals advance their agenda with policies that reflect current economic thinking?

But Mr. Chait opts instead for conspiracy mongering. In trying to explain what he considers wrong with politics today, he goes off the rails with an extended blogrant of a book that focuses on personalities and name-calling rather than substance, and is replete with the sort of factual errors that come from sloppy handling of secondary sources.

Mr. Chait contends that a tiny cabal of zealot “supply-siders” has so bludgeoned the Washington establishment in support of “tax cuts for the rich” that the nation’s political elite has a case of Stockholm syndrome, in such thrall to these advocates that they are impervious to rational debate and unwilling to exercise the will of the American people. Mr. Chait attributes sundry and extreme views to those supply-side terrorists — “tax cuts pay for themselves” — and spends much of the book attacking the straw men he sets up.

If Mr. Chait’s goal is entertainment, he succeeds. But he misses the chance to explore how economic thinking has changed since 1968, or even since 1948, when MIT’s Paul Samuelson, an economic adviser to Kennedy and Johnson, wrote his famous textbook “Economics: An Introductory Analysis.” Back in those days, academic theory held that government spending could keep the economy humming at full employment through the astute management of aggregate demand, so that a progressive tax system could siphon off ever more resources to support worthy government programs ranging from the Vietnam War to housing subsidies.

One could say that the practical experience of stagflation in the 1970s killed this vision, but the field of economics has also matured in the intervening decades. Where academic Keynesianism in the 1960s had emphasized demand management above all else, new work in microeconomics showed that incentives at the margin do matter, and that deadweight efficiency losses result when government spends money both on the tax and on the spending side of the equation. No economist on the planet questions this effect. Whereas government spending once had seemed stimulative, because government had no marginal propensity to save, the new thinking suggested that pure friction canceled out at least some of the vaunted Keynesian multiplier effect — and in any case, demand management alone could not override the business cycle or sustain economic growth over the long term.

What’s more, while economists may debate the optimal level of taxation in the United States, given the current requirements of public finance, economists universally agree that in principle, low taxes are better than high taxes, taxes above the optimal level are damaging to the economy, deadweight losses result from bad tax policy, and the best tax system is one with a broad base and low tax rates. If this makes you a “supply-sider” in Mr. Chait’s lexicon, he has a problem with the entire economics profession.

Plenty of other liberals are offering more constructive visions of the future, in which higher taxes more efficiently collected provide revenue for what they see as essential social programs, and others, notably Elaine Kamarck of the Kennedy School, argue that liberals can find effective ways to deliver social benefits without the bureaucratic structures conservatives have critiqued so trenchantly. It would have been interesting to see a writer with Mr. Chait’s talents take these arguments to a broader public. Instead, for liberals, his book is a missed opportunity.

Mr. Lucier, an analyst, has followed tax, economic, and regulatory policy in Washington, D.C., for more than 25 years.