Reasonable people are making reasonable arguments for and against Barack Obama, Hillary Clinton, and John McCain. But in a recent column attacking Barack Obama, Paul Krugman has lost his bearings.

Krugman objects to Obama's suggestion, on Fox News, that he accepts the Republican claim that regulation should take the form of tradable emissions permits rather "top-down command and control." Krugman says that Obama is "giving Republicans credit for good ideas they never had."

Here is what Obama actually said:

"I think that back in the '60s and '70s a lot of the way we regulated industry was top-down command and control, we're going to tell businesses exactly how to do things. And you know, I think that the Republican Party and people who thought about the markets came up with the notion that, 'You know what? If you simply set some guidelines, some rules and incentives, for businesses--let them figure out how they're going to, for example, reduce pollution,' and a cap and trade system, for example is a smarter way of doing it, controlling pollution, than dictating every single rule that a company has to abide by, which creates a lot of bureaucracy and red tape and oftentimes is less efficient."

Krugman objects, "Mr. Obama's answer was puzzling because he gave credit where it isn't due."

Actually Obama had it right. As Harvard's Robert Stavins, a long-time participant in the relevant debates and perhaps the world's leading expert on what actually happened, wrote me, "I think I know the history and provenance of U.S. of cap-and-trade and emission-reduction-credit systems relatively well, and Krugman's column is exceptionally misleading."

The major emissions trading program in federal law, enacted in 1990 and focused on acid deposition, was developed under Bush 41, in the White House no less (under the leadership of C. Boyden Gray, an influential Republican and a pioneering figure, in political circles, with respect to emissions trading). The law was pushed through an initially skeptical Democratic-controlled Congress. The pivotal role of the Bush White House has been carefully documented in books and articles. (See, for example, A. Denny Ellerman et al., Markets for Clean Air.)

The several early emissions trading systems, adopted in the 1970s, were established in Republican administrations (Nixon/Ford), with significant opposition from Democrats (and environmental organizations). The trading program for lead in gasoline was also adopted under a Republican president (Reagan).

Krugman is quite right to say that the Reagan administration resisted a regulatory response to acid deposition (a point that is irrelevant to Obama's claims). He is also right to say that economists of all stripes supported tradable permit systems by 1990. But in the political domain (which was clearly the topic), Obama was correct to say that such systems have come from Republicans. As Robert Stavins writes, "the history is what it is, and unfortuately Krugman has misled his readers in order to score some political points."

There is a more general point here. Krugman wants Democrats to attack Republicans and to call them "the party of denial," rather than to give them credit for good ideas. But where credit is due, it is not exactly terrible to give credit.

--Cass Sunstein