I lean toward McCain winning. McCain TTL is not going to run a campaign like the McCain of 2008 OTL and voter fatigue is gonna hurt the Dems. Plus, Gore will get much more scrutiny over 9/11 (if it still happens, I still think it would unfortunately as it was in the works for years) than Bush did because the Democrats would've been in power for over 8 years if it happened and Clinton oversaw 2 attacks from al Qaeda abroad, Bush had the excuse of "I just Got here," and also because Gore doesn't isn't going to have the folksy swagger/ tough guy image that Bush made for himself after 9/11. I do however think Gore would respond to the attacks better than Bush did, as there would most likely be no Iraq war and Gore would commit more time and resources to the fight against Al Qaeda.
Economically, the recession of 2001 still happens and the recovery still probably doesn't take off until mid 2003 like OTL, and will probably be as weak as OTL. It'll basically be the Bush economy with lower debts and deficits, as if he passes one at all, Gore will only pass a middle class tax cut, not two of the biggest tax cuts like Bush did, and no Iraq war means less defense spending. Also, if Medicare Part D happens at all, it'll be more funded than it was OTL.
If Gore wins in 2000, it's close. In OTL, he ran a terrible campaign and because of that in my opinion, snatched defeat from the jaws of victory given how good we thought things were at the time. I don't see him running a better campaign in 2004 TTL and I can see McCain being a much better and more centrist candidate than he was in 2008 OTL, he'll be more like he was in 2000 against Bush. It'll be pretty close, but I give it to McCain. 2008 will be a tossup in this scenario because while I think the collapse still happens, it might happen later than OTL without Bush as President. If it does happen at the same time as OTL however, McCain is screwed with a capitol S.