At least to my mind, last week was extremely significant. Last week, George W. Bush for the first time believably acknowledged that human beings are the principal cause of global warming.
Now, I know, I know: There are a few instances from the past where if you listen really, really closely, Bush sorta kinda said as much. But then he would come out and say something else different and contradictory–or Dick Cheney would.
Or Bush would get revealed to have gotten his science advice from Michael Crichton.
Anyways, something would always happen to make you slide the administration right back into the “skeptic”/denialist camp again.