Barack Obama wants you to know that nuclear power is good for you. He really and truly does.

He’s warned of “the worst consequences of climate change” unless new nuclear plants sprout from the land. And of countries like China eating our technological lunch. And of unemployment getting even worse, due to the loss of good, green jobs. And of nothing less than “our economy, our security, and the future of our planet” being at risk.

He’s announced $8.3 billion in federal-loan guarantees to build a pair of nuclear reactors in Georgia (the first in the U.S. in more than 30 years), and said there will be plenty more where that came from. He’s appointed as energy secretary a Nobel laureate who’s pledged to “aggressively” expand nuclear power; nominated as his new commerce secretary the ex-C.E.O. of a power company that thought the world of its nuclear plants (including the two on the California coast adjacent to earthquake faults); and had successive White House energy czarinas who use the modifiers “safe, clean, reliable” when speaking of nuclear power — exactly like the ads of the industry’s trade association.

And what has Barack Obama gotten for his efforts? Trouble on all fronts.

The Greens are apoplectic at his “disastrous” . . . “nightmare” . . . “sell-out” policy, to quote the headlines of their blogs and articles. The polls, which used to report record-high approval of building U.S. nuclear plants, have switched to record-high disapproval—courtesy of the tsunami that left four reactors bathing northern Japan in radiation not seen since Nagasaki. And the Georgia loan guarantee? Turns out that the Nuclear Regulatory Commission hadn’t approved the safety of the reactor design (it still hasn’t); the project owner is one of the worst-polluting major power-plant companies in the world; and Energy Secretary Steven Chu—whose department oversees the guarantee program—had never heard of the “well above 50 percent” default rate projected by the Congressional Budget Office until reporters told him.

The capper: the same people who wooed Obama into being the nation’s chief advocate of spreading nuclear power now want no part of it.

How could such a smart guy have gotten into such a big mess?

A good slice of the answer has to do with Exelon, a utility company headquartered in Chicago with $18.6 billion in annual revenues, and America’s leading provider of nuclear-generated electricity.

Exelon is an enterprise of superlatives. It owns the largest “nuclear fleet” (17 reactors including seven General Electric Mark I models—the same type that formerly powered Fukushima Daiichi 1, 2, 3, and 4), turning out roughly 20 percent of all nuclear-generated electricity in the U.S. The 10 facilities dedicated to this activity include the country’s first (and after 43 years, now oldest) large-scale, commercially owned nuclear power plant, and TMI 1, surviving twin of the country’s most infamous, Three Mile Island 2. Exelon’s nuclear operations are counted the safest, most efficient, and most environmentally responsible in the industry. This, though, may be a tough sell in South Jersey, where in 2009 an Exelon nuclear plant leaked radioactive tritium into aquifers supplying the drinking water of more than one million residents.

As for political clout, it’s summed up by how Exelon’s former chief Washington lobbyist, Elizabeth Moler (who served as deputy national co-chair for the Obama campaign), described her employer to Forbes: “the President’s utility.”

How Exelon acquired that title—and in the process changed the fortunes of Rahm Emanuel, David Axelrod, and State Senator Barack Obama, is—like the workings of nuclear power plants—complicated.

The simplified version skips several twists. Such as: Thomas G. Ayers—father of retired Weatherman bomber Bill Ayers—having once been C.E.O. of Exelon forebear Commonwealth Edison; Bill’s wife, 60s *über-*radical Bernardine Dohrn, and future First Lady Michelle Obama overlapping as associates at ComEd’s principal outside legal counsel; and two other coincidences—recent Harvard Law grad Barack chairing a public-education group his friend Bill helped found, and both men serving as board members of a private anti-poverty foundation.