A trio of US senators had planned to roll out a long-awaited climate bill today, one that would provide the last-best hope for global warming legislation this year. Instead, Massachusetts Democrat John Kerry, Connecticut Independent Joe Lieberman and South Carolina Republican Lindsay Graham find themselves struggling to revive climate talks that faltered last week when Democratic congressional leaders announced plans to pursue immigration first.

Interpretations span the spectrum (more here), with some saying the issue is dead for the year and others citing evidence that the talks are closer than ever. Both may be true to a certain extent, but the biggest constraint is time. The Senate has three months before the August recess, at which point conventional beltway theory suggests senators will turn entirely to the November elections. In that narrowing window, Democrats must finish up with financial reform, push through a new Supreme Court nominee and tackle spending bills.

Graham, who has the lonely job of spearheading the effort on the Republican side, says a Democratic shift toward immigration – an issue that lawmakers haven’t even touched up until now – would effectively kill the climate bill. Given that immigration doesn’t stand a chance of moving forward, Graham accused Democrats of abandoning work on real issues in order to court Hispanic voters prior to the elections. As such, he said, he too, would walk away.

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The game is not over, to be sure. Senate Democratic leader Harry Reid – who faces a tough reelection battle in a state that has a fare share of Hispanic voters – has backed off and said he will bring up whichever bill is ready first. And that brings us to the most important question: how close are they? The trio needs 60 out of 100 votes to overcome legislative hurdles and get a bill through, and that’s a hurdle that many experts say is still out of reach.

Graham’s point, backed by many environmentalists and supporters of climate legislation, is that the deal isn’t going to fall in the Democrats’ lap. What’s keeping it alive at the moment is the fact that there are good reasons for both sides to strike a deal (for more on that, see Steven Pearlstein’s earlier column in the Post). Democrats could lose ground in the elections later this year, which would only make a deal more difficult, and business interests are basically playing Russian roulette with the Obama administration, which could roll out its own greenhouse gases regulations next year (to be followed by lawsuits and ultimately a court ruling).

The fact that there is even talk that the deal might be backed – or at least not actively opposed – by the oil industry and other business interests is significant, but that only goes so far. Indeed, most would agree when Graham says that Senate leaders and President Barack Obama will need to fully engage – in the same way that they did health care – if they want to get a bill through this year.