If there’s a news-dominating name that isn’t Trump, it’s Putin. But as much as we have come to know about America’s president, popular knowledge of Russia’s leader seems limited to a few snapshots of a strongman — bare-chested on a horse, or striding with dark purpose toward a podium. Yes, he used to be a KGB spy, but just who is this guy?

Enter Richard Lourie, who has all the Kremlinological credentials to set us straight. Biographer of Stalin and Sakharov, former consultant on Russia to Hillary Clinton, and Mikhail Gorbachev’s translator for The New York Times, Lourie takes the autocrat’s measure in his hot new book, Putin (Thomas Dunne Books, 224 pp.,  **½ out of four stars). With its predictive subtitle, His Downfall and Russia’s Coming Crash, Lourie also takes a leap of expert judgment.

His thesis is that Putin, who came to power in 2000, has squandered his opportunity. After the breakup of the Soviet Union and a sharp, chaotic turn from ossified Communism to a free-booting market culture — with oligarchs skimming billions and former Soviet countries becoming Russia’s rivals — Putin has “reverted to the tried and true, in his case ‘the power vertical,’ ” Lourie concludes.

Rather than transform Russia into a broadly engaged, knowledge-based society that would mean more jobs for the masses and a more agile future, Lourie’s Putin has been content with a house-of-cards economy based on Russia’s oil and gas bounty, and with old-school imperial ambitions.

Lourie begins in Leningrad, where Vladimir Vladimirovich Putin — “Volodya” — was born in 1952, kept his head down at KGB school, mastered sambo (a Russian form of judo), and got to Moscow just in time to rise to power, quietly and inscrutably, while the old USSR was falling apart. Now, everywhere from the NATO countries, Ukraine and Crimea, to Kazakhstan and central Asia, Putin casts an opportunistic but less than visionary eye, Lourie tells us.

He believes it’s all too late for the aging spymaster (he’s 64), as oil prices stagnate and authoritarianism breeds revolt, chasing Putin into exile, or worse, before long. No wonder Putin signed into existence a personal army of…