Their ample empirical evidence, some of which I’m citing here, proves that America’s ever-widening income inequality was not an inevitable by-product of the modern megacorporation, or of globalization, or of the advent of the new tech-driven economy, or of a growing education gap. (Yes, the very rich often have fancy degrees, but so do those in many income levels below them.) Inequality is instead the result of specific policies, including tax policies, championed by Washington Democrats and Republicans alike as they conducted a bidding war for high-rolling donors in election after election.

The book deflates much of the conventional wisdom. Hacker and Pierson date the dawn of the collusion between the political system and the superrich not to the Reagan revolution, but to the preceding Carter presidency and its Democratic Congress. They also write that contrary to the popular perception, America’s superhigh earners are not mostly “superstars and celebrities in the arts, entertainment and sports” or the stars of law, medicine and real estate. They are instead corporate executives and managers  increasingly (and less surprisingly) financial company executives and managers, including those who escaped with outrageous fortunes as their companies imploded during the housing bubble.

The G.O.P.’s arguments for extending the Bush tax cuts to this crowd, usually wrapped in laughably hypocritical whining about “class warfare,” are easily batted down. The most constant refrain is that small-business owners who file in this bracket would be hit so hard they could no longer hire new employees. But the Tax Policy Center found in 2008, when checking out similar campaign claims by “Joe the Plumber,” that only 2 percent of all Americans reporting small-business income, regardless of tax bracket, would see tax increases if Obama fulfilled his pledge to let the Bush tax cuts lapse for the top earners. The economist Dean Baker calculated that the yearly tax increase at the lower end of that bracket, for those with earnings between $200,000 and $500,000, would amount to $700  which “isn’t enough to hire anyone.”

Those in the higher reaches aren’t investing in creating new jobs even now, when the full Bush tax cuts remain in effect, so why would extending them change that equation? American companies seem intent on sitting on trillions in cash until the economy reboots. Meanwhile, the nonpartisan Congressional Budget Office ranks the extension of any Bush tax cuts, let alone those to the wealthiest Americans, as the least effective of 11 possible policy options for increasing employment.

Nor are the superrich helping to further the traditional American business culture that inspires and encourages those with big ideas and drive to believe they can climb to the top. Robert Frank, the writer who chronicled the superrich in the book “Richistan,” recently analyzed the new Forbes list of the 400 richest Americans for The Wall Street Journal and found a “hardening of the plutocracy” and scant mobility. Only 16 of the 400 were newcomers  as opposed to an average of 40 to 50 in recent years  and they tended to be in industries like coal, natural gas, chemicals and casinos rather than forward-looking businesses involving the Green Economy, tech or biotechnology. This is “not exactly the formula for America’s vaunted entrepreneurial wealth machine,” Frank wrote.

As “Winner-Take-All Politics” documents, America has been busy “building a bridge to the 19th century”  that is, to a new Gilded Age. To dislodge the country from this stagnant rut will require all kinds of effort from Americans in and out of politics. That includes some patriotic selflessness from those at the very top who still might emulate Warren Buffett and the few others in the Forbes 400 who dare say publicly that it’s not in America’s best interests to stack the tax and regulatory decks in their favor.

Many of the countless tasks that need to be addressed to start rebuilding an equitable America are formidable, but surely few, if any, are easier than eliminating a tax break that was destined to expire anyway and that most Americans want to see expire. Two years ago, Obama campaigned on this issue far more strenuously than he did on, say, reforming health care. Now he and what remains of his Congressional caucus are poised to retreat from even this clear-cut battle. You know things are grim when you start wishing that the president might summon his inner Linda McMahon.