I am generally hesitant to look back on history and say, "If only X hadn't happened, everything else would have been great." People tend to do that about the Kennedy assassination, Neville Chamberlain's capitulation to Hitler, Napoleon's invasion of Russia, that one boy/girl you should/shouldn't have made a pass at in high school, etc. It's a counterfactual nightmare that can drive you mad.
That said, it's hard not to look back on the 2000 presidential election as the poison fruit from which the rest of the crappiness of the past decade grew. It's tempting to say, as Yglesias does, that, had a few tiny things in Florida been different that fall, the rest of the decade would have been astonishingly different. The Gore response to 9/11 (if the 9/11 attacks had even been successful) would surely have been different, and there would have been no war with Iraq. And no elimination of the estate tax. And a better federal response to Hurricane Katrina. And no abandonment of environmental goals. And so on.
On the other hand, it's extremely rare for a party to hold onto the presidency for four consecutive terms. Gore might well have lost in 2004, producing a President McCain? Romney? Cheney? And maybe with a Republican House and Senate? Who knows?
Okay, I'm back to my original point. Best not to think about this stuff.