As soon as President Barack Obama finished outlining his plan to fight climate change by sidestepping Congress, the unblinkingly pro-market Competitive Enterprise Institute issued a statement denouncing his approach as "undemocratic" and "bordering on authoritarian." I never thought I'd write this, but CEI raises a good point: What makes it OK to sidestep Congress?

Nobody's arguing that Congress has to agree with every little thing the president does for his actions to be legitimate. But on an issue that touches almost every part of the economy and shapes the way we live, it's hard to dismiss Congress as just one more spoiled interest group. So if unilateral executive action goes against the will of Congress, which represents the people just as much as the president does, what's the basis on which Obama can claim popular legitimacy for his approach?

There are plenty of good arguments in favor of Obama taking unilateral action on climate change. First, environmental necessity: Every day we wait makes the problem worse and puts the planet at greater risk. Let's call this the "we can't wait" argument.

Second, Republicans in Congress have made clear that they won't cooperate with the president on a plan to curb carbon emissions. We could debate the reasons for that (Rabid partisanship? Business interests run amok? Troglodyte disease?). Regardless, Obama reasonably concluded that it's unilateral action or nothing. Let's call this the "no alternatives" argument.

Third, Obama is using the means available to him as the head of the executive branch. He's not doing anything illegal, and if he was, any legal challenges would eventually be decided by the courts. Let's call this one the "legally permissible" argument.

The problem is that none of those arguments address the critique that CEI is making. To do so, you need to resort to one of two points. And, if we're being honest, neither is terribly satisfying.

The first is that if voters decide they don't like Obama's approach to regulating carbon, they can punish whichever Democrat runs to replace him. Of course, 2016 is a long way off, and Obama will have had time to implement much of this agenda by then.

The second answer is that the president's prerogative includes the responsibility to weigh two competing bad options and choose the lesser one. By this count, he doesn't need to contest opponents' arguments that the will of Congress ought to be respected; he only needs to note that failing to fight climate change by whatever means possible would be the greater evil.

Of course, democratic legitimacy is all about who has the power to choose between competing priorities, and establishing a process to constrain that power. You can support Obama's proposals with all your heart and still be concerned that he's doing an end-run around Congress to get there.

(Christopher Flavelle is a member of the Bloomberg View editorial board. Follow him on Twitter.)