These are my five scenarios for a McCain/Hillary matchup.
This is the best McCain can do nationally, and it happens because the War in Iraq improves even more, and the economy doesn't change much from its current levels. He also hits Clinton hard with ads and attacks, she does poorly:
McCain wins 355 to 183 in a landslide.
My second one is where the national situation acts the same as the first scenario, but Clinton's campaign does about as well, as McCain's, and fights it out fairly well with McCain:
McCain wins 311 to 227
This scenario is the most likely, where the situation in the economy worsens, and the Iraq War stays about the same, but McCain still outperforms Clinton by a little because of his maverick status and independent appeal:
Clinton squeaks it out 275-263
The next scenario is where the national situation stays the same, as the third scenario, but Clinton's campaign outperforms McCain and really hurts him on the War In Iraq and some of his more radical War on Terror comments:
Clinton wins 304-234
This is Clinton's best case scenario where the Iraq War slightly worsens, and the Economy goes into a fairly severe recession, with a minor stock market crash. She also attacks McCain harshly and defeats him in the two debates:
Clinton wins 360-178