In recent years in all countries the greatest effects have been shifting the centre pole of the debate. Often this has been to the right economically, Germany's centre-left SPD adopting privatising agendas, and in the UK Labour selling off sections of the National Health Service, although the Tories adopting more liberal social stances is an example that it can work both ways too.
In the US the Republican Party have done this incredibly well (from their perspective), and now many Democrat candidates follow a more right-wing line on many issues than in the past.
Climate change has not really raised its head so far in the US election, a survey of of talk shows counted 2,275 questions asked of presidential candidates over the past year and found that just three mentioned global warming. Iraq, immigration and health care seem to be taking a much more central role. However, later in the year this may well change, and if it does, that centre pole is really going to matter.
In the past climate change has been an issue to avoid; it didn't have a huge number of people who knew much or supported the issue strongly, and a candidate supported action was a huge target for attack. Now it's much further up the agenda and can only go up. Who the republican candidate is will determine the manner of the discussion.
If it's any candidate but McCain it will follow the typical "hurting US jobs", "disputed", "EU conspiracy theory" (take your pick) route it always has. If McCain gets the nomination, suddenly it's no longer about all the questions that were actually answered 10 to 20 years ago, now it's about the best way to tackle it. That we should have real significant emission reductions will not feature in the debate; it will be an accepted viewpoint to start from (unlike even at Bali). This would be a great leap forward as all the media will have to follow along with this. It could start the re-definition of climate change as an issue in the US mainstream.
As none of the main Democrat candidates have a fantastic record on the subject (cap and trade is good, but 15% by 2020 is crap, even if they don't sell out), I believe that the result of the Republican nomination is far more important.
So, fingers crossed for McCain right now.
(UPDATE: I did actually post this yesterday before the result but ended up posting it to the wrong place. Glad to hear the New Hampshire result though.)