Just five days out, a new batch of polling offers little evidence that Mitt Romney can overcome President Obama’s small but persistent swing-state edge. And polling guru Nate Silver, who has long said an Obama win is likely, is now putting his money where his pixels are.

Obama leads his Republican challenger by 50% to 44% in Iowa, according to an NBC News/Marist College/Wall Street Journal poll released Thursday morning.

The same poll shows a tighter race in Wisconsin and New Hampshire. Obama leads by 49% to 46% in the Badger State, and 49% to 47% in the Granite State.

Thursday morning, after Nate Silver’s probability of Obama winning ticked up to 79%, the New York Times statistician tweeted at msnbc’s Joe Scarborough, who has been more bullish on Romney’s chances: “If you think it’s a toss-up, let’s bet. If Obama wins, you donate $1,000 to the American Red Cross. If Romney wins, I do. Deal?” Scarborough has yet to respond.

Silver has been criticized lately by some conservative pundits and data-averse campaign reporters for consistently forecasting an Obama victory—even though the other leading data-based polling analysts have made similar predictions, and some show an even stronger chance of an Obama win.

The Romney camp is certainly talking a good game lately. “Obama has a political environment problem,” campaign pollster Neil Newhouse told reporters on a conference call Wednesday. “He’s got an intensity problem, he’s got an image problem and he’s got a ballot problem — and they all add up to a challenging Tuesday next week.”

“Right now their firewall is burning,” added political director Rich Beeson.

But the facts paint a less rosy picture.

Iowa and its six electoral votes appear increasingly likely to end up in the president’s column. He has lately opened up a lead there in most of the leading poll trackers. He’s also boosted by early voting: In the NBC poll, 45% of respondents said they’d already voted or planned to. Among those voters, Obama holds a 62-35% edge. And Obama boasts a strong ground game in the Hawkeye State, a legacy of his crucial 2008 primary victory in the state. Romney, by contrast, failed to win Iowa’s primary in both of his nomination fights.

If Obama were to win Iowa and Ohio, where polling also looks relatively strong for him, he’d need only to carry the blue-leaning states that John Kerry won in 2004—and could even lose New Hampshire—to get to 270 electoral votes. And that’s without Nevada’s six electoral votes, which recent polls suggests are likely headed his way too.

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Still, among the states he’d need is Wisconsin, with its ten electoral votes, where the NBC poll is only the latest of several to show a tight race. The Romney campaign has been sounding bullish on the Badger State lately: It’s hoping to use Paul Ryan to exploit a home-field advantage there, as well as to take advantage of a strong GOP turnout operation that carried Gov. Scott Walker to victory in this summer’s recall election. Still, a Marquette University poll released Wednesday—and considered the gold standard of pollsters in the state—found an eight-point Obama advantage, and he remains the clear favorite.

In addition to Wisconsin, Romney is making a late play for three other blue-leaning states which would serve just as well or better: Pennsylvania, Minnesota, and Michigan.

His campaign surprised analysts this week by running TV ads in the first two—a move the Obama campaign is countering with ads of their own—and there are fears among Democrats that Hurricane Sandy could depress Election Day turnout in Philadelphia. But Romney’s chances in these three states appear even slimmer than in Wisconsin. A Michigan poll released Wednesday showed Obama up by 6 (another showed a narrower 3-point edge for the president), and Romney has consistently trailed in polls of both states.

As Silver wrote Thursday in a post titled “Obama’s Electoral College ‘Firewall’ Holding in Polls”: “[F]or Mr. Romney to win Michigan, Minnesota, or Pennsylvania, the polls would have to be much further off than they are in Ohio.” David Axelrod, Obama’s top campaign strategist, was blunter on Morning Joe Wednesday, saying he’d shave his mustache if Romney won any of the three states.

That leaves a relatively bleak picture for the GOP challenger. Even if he wins Florida, Virginia, and Colorado—all of which appear to be tossups right now—he’ll need to pick off at least one state where he’s consistently been behind throughout the race.

That’s not impossible, and it’s worth noting that the national polls continue to show essentially a tied race. But it’s a tall order. Perhaps Silver knows what he’s doing after all.