Did a climate bill ever have a chance to squeak through Congress? Could anything have saved it? Politico's Darren Samuelsohn has a piece today about the usual, tiresome round of recriminations among greens after Harry Reid killed cap-and-trade. (Okay, technically Reid's putting it off until after August recess, but the odds of survival are grim.) The underlying question, though, is a good one: Peering back over the past two years, there were a few pivot points where things might have turned out very differently.

What if McCain had won the election? If McCain had won in 2008, with Democrats controlling both the House and Senate, then it's quite possible we'd have a climate bill by now. McCain, after all, supported cap-and-trade on the campaign trail—he only reversed himself after he lost the election (see here for a few theories on that). Republicans would have had a much trickier time demonizing the policy as a—what's the phrase?—"job-killing energy tax," and most Democrats would have backed it. Now, would McCain's proposal have been ideal? Nope. His preferred iteration of cap-and-trade was weaker than Obama's and rife with corporate giveaways. McCain also would have opposed a variety of crucial side measures, such as efficiency standards. But the end result might have been better than, well, nothing.

Then again, these counterfactuals are never so simple. A president McCain might have also vetoed any sort of stimulus bill, which would have deepened the recession and made it that much harder to enact any environmental legislation. And who knows whether McCain would have pursued the EPA's authority under the Clean Air Act to regulate greenhouse-gas emissions—which, remember, is currently the most powerful tool the United States has to fight global warming.

What if climate had come before health care? If you put the two problems side by side, global warming seems like a much more urgent problem than health care. Don't get me wrong, 45 million uninsured is an utter travesty. But the chance that we're on course to render big chunks of the planet uninhabitable sort of eclipses that. Each year the United States delays tackling its emissions means another year in which more carbon is spewing into the air, nudging temperatures upward. After enough dithering, we'll reach a point in which the worst effects of climate change are locked in and it becomes impossible to avoid catastrophe. Health care, meanwhile, can be fixed at any time—the relevant problems are never irreversible. That's a good reason for doing climate first rather than procrastinating until right before the midterms.

That's exactly what Nancy Pelosi did in the House, making sure the climate bill got passed in 2009. But the Senate and the White House wanted to focus on health care. That was understandable: Universal health care has been the single biggest Democratic policy priority for the last half-century. A more opportune moment might never arise. Plus, there's no guarantee that a climate bill could have garnered 60 votes in the Senate if it had come up for a vote after the stimulus. Cap-and-trade might well have crashed regardless—and dragged down the chances for health care and financial regulation with it.

What if Obama had made climate a bigger priority? A lot of green groups have been lobbing around this criticism of late, as Tim Dickinson documents in Rolling Stone. The president, they argue, never stepped in and barnstormed for a climate bill the way he did with health care. Obama's BP oil spill speech was lifeless on the topic of global warming. He was afraid to make the case for cap-and-trade publicly. He never locked senators in a room and forced them to come to an agreement. The White House was reluctant to dominate the legislative process, in part because some advisers thought the bill would fail no matter what, and they didn't want to be responsible for that failure. Could a more assertive Obama have made a difference? I wonder. There weren't 60 votes in the Senate for cap-and-trade, and White House pressure didn't seem to work on potential swing votes like Scott Brown. This one may well have been beyond the president's control.

What if Democrats had started with a more modest bill in the first place? There's plenty of reason to support an economy-wide cap-and-trade system—for all its flaws, it's a flexible market-based system for wrestling down greenhouse-gas levels. But we're not likely to get one now. And the failure of cap-and-trade has imperiled all the other "complementary" measures that could have helped make progress chipping away at carbon pollution. Like the renewable energy standard. Or efficiency rules. What if Democrats had tried an "energy-only" bill from the start, sans cap-and-trade? (Some moderates like Byron Dorgan and Jeff Bingaman counseled this course.) Would Congress have ended up passing a less substantial bill than what greens wanted but a more meaningful bill than what's on the table now—i.e., virtually nothing?

That's tough to say. It's hard to fault environmental groups for pushing for cap-and-trade. For awhile, Republican Lindsey Graham really did seem sincere about sponsoring a major climate bill. And, while he couldn't bring any other Republicans along, that was at least a decent starting point. Still, with the benefit of hindsight, it's natural to wonder whether a more modest initial bill—say, a utility-only cap plus a renewable standard plus efficiency—might've led to more success in the end.