It seems safe to say that “Capital in the Twenty-First Century,” the magnum opus of the French economist Thomas Piketty, will be the most important economics book of the year — and maybe of the decade. Mr. Piketty, arguably the world’s leading expert on income and wealth inequality, does more than document the growing concentration of income in the hands of a small economic elite. He also makes a powerful case that we’re on the way back to “patrimonial capitalism,” in which the commanding heights of the economy are dominated not just by wealth, but also by inherited wealth, in which birth matters more than effort and talent.

To be sure, Mr. Piketty concedes that we aren’t there yet. So far, the rise of America’s 1 percent has mainly been driven by executive salaries and bonuses rather than income from investments, let alone inherited wealth. But six of the 10 wealthiest Americans are already heirs rather than self-made entrepreneurs, and the children of today’s economic elite start from a position of immense privilege. As Mr. Piketty notes, “the risk of a drift toward oligarchy is real and gives little reason for optimism.”

Indeed. And if you want to feel even less optimistic, consider what many U.S. politicians are up to. America’s nascent oligarchy may not yet be fully formed — but one of our two main political parties already seems committed to defending the oligarchy’s interests.

Despite the frantic efforts of some Republicans to pretend otherwise, most people realize that today’s G.O.P. favors the interests of the rich over those of ordinary families. I suspect, however, that fewer people realize the extent to which the party favors returns on wealth over wages and salaries. And the dominance of income from capital, which can be inherited, over wages — the dominance of wealth over work — is what patrimonial capitalism is all about.