Whenever you hear a politician start a sentence with, "If we can put a man on the moon ... ," grab your wallet.

For years, Democrats, enthralled by the cargo cult of the Kennedy presidency, have used the moon landing as proof that no big government ambition is beyond our reach.

The latest example of anthropogenic-lunar empowerment is global warming. Al Gore and Barack Obama routinely cite the Apollo program as proof that we can make good on the president's messianic campaign pledge to stem the rising ocean tides and hasten the healing of the planet.

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The problem with the "if we can put a man on the moon, we can certainly spend trillions on this or that" formulation is that it sees political and scientific accomplishments as interchangeable. The moon landing was a daunting but nonetheless discrete challenge. Throw in enough brainiacs and blank checks -- and heroes willing to risk their lives -- and it was almost foreordained that someone would make that small step for man and that giant leap for mankind.

But politicians see things through a political lens -- every great accomplishment looks like a political accomplishment. Kennedy cultists seem to think that JFK's pledge succeeded in part because he was eloquent and inspiring and popular. No doubt all that helped. But if Kennedy had promised that by the end of the decade America would have a fully functioning perpetual motion machine, his grand challenge would be remembered as a joke.

Recall that Kennedy's successor, with far more political capital than Kennedy had, promised to defeat poverty. Historian Steven Hayward notes that in 1966, Lyndon Johnson's commander in the War on Poverty, Sargent Shriver, told Congress that the White House believed poverty in America would be eliminated within 10 years. "Why," Hayward wryly asks, "should social science be more difficult than rocket science?"

I don't know that one is more difficult than the other, but I do know that they are not interchangeable. Physics is good at figuring out how to split atoms. Sociology, not so much.

Obama seems to be on both sides of the lesson. The president says he wants to invest massively in scientific research, eventually spending 3 percent of gross domestic product on scientific R&D, with a big chunk devoted to energy research. Who knows? That might work. Continued...