For John McCain, everything seems to hinge on Pennsylvania. If he wins that state, he has a real chance to win the White House. But if, as expected, Barack Obama wins it, then McCain has little or no hope.

The good news for McCain is that his campaign's efforts in the state appear to be paying off, at least to an extent. It's one place where we actually can say that the polls appear to be tightening, though as Pollster.com's Mark Blumenthal noted, "most of the change in Pennsylvania involves an increase in McCain's support -- from 40.3% to 43.8% -- while Obama has lost just a single point on our estimate." Obama still remains above 50 percent in most polls there, which means that even a last-minute surge of undecided voters breaking overwhelmingly for the Republican wouldn't be enough to turn the blue state red.

For the sake of argument, though, let's say that McCain does manage to pull it off. That still leaves Obama with several ways he can win the White House.

McCain's campaign has reportedly written off Colorado, Iowa and New Mexico, at least privately. They continue to make noise about Iowa being in play, but it's been looking pretty solid for Obama this year, and the latest poll from the Des Moines Register shows Obama leading by an astonishing 17 percentage points, 54-37. So let's put those three states in Obama's column and Pennsylvania in McCain's. With that done, Obama would still win in any of these scenarios:

• He wins Florida
• He wins Ohio
• He wins Virginia plus any one of Georgia, Indiana, Missouri, Nevada or North Carolina
• He wins North Carolina plus any one of Georgia, Indiana, Missouri, Montana, Nevada, North Carolina, North Dakota or Virginia

Now, it is unlikely that Obama would win some of those states -- Indiana, Missouri, Montana and North Dakota, specifically -- and not win Pennsylvania. (Indeed, if he does win any of those states, it would most likely be a sign of a big blowout. Georgia, too, seems like a longshot, but its demographics are much different than Pennsylvania's, so it's conceivable that he could manage to win Georgia but not Pennsylvania.) But I include them simply to show how precarious McCain's situation would be even if he did manage to grab that prize.

See the map differently? Tell us your scenarios in the comments section.