Word of a new TV adverstising buy here in Maine underscores just how close Mitt Romney's campaign believes the presidential election may end up being. Restore Our Future, a pro-Romney Super PAC, will begin airing more than $300,000 in television spots in the Portland-Auburn, Bangor and Presque Isle markets later this week. Unlike in most states, the winner of the overall presidential vote in Maine doesn't automatically get to walk away with all the electoral votes. Jay Field explains how the system works here and why Romeny allies are sprending money in the state's 2nd Congressional District.

So Maine has four electoral votes - not a ton, but in a close election, every electoral vote is like a little piece of gold. Two of them - the ones that every state gets for having two U.S. Senators - they go to the presidential candidate that wins the overall statewide vote. The other two, one each for Maine's 1st and 2nd Congressional Districts, go to the candidate that wins the most votes in those districts.

"Barack Obama is going to come out ahead in the first CD, and he's going to come out ahead statewide here," says Professor Mark Brewer, who teachers political science at UMaine-Orono.

Brewer says the electoral vote in the 2nd Congressional District is up for grabs. "Maine is such a cheap television date, you're almost crazy not to dump some money in there," he says.

And for months, there were rumors that the Romney campaign or its allies would do exactly that. Now, locked in a nail-biter of a race, a super PAC backing the Republican candidate has opened the floodgates. From Oct. 25 through the Oct. 29, Restore Our Future will spend more than $300,000 on ads in the Portland-Auburn, Bangor and Presque Isle markets.

David Sorenson says Romney is running ahead of President Obama in the 2nd Congressional District by around five points. Sorenson is communications director for the Maine Republican Party.

"Romney's numbers are very strong," he says. "The people of morthern Maine are just fed up. They're worse off than they were four years ago and they want to focus on jobs. It's a 'red' district."

Democrats, though, beg to differ. Congressman Mike Michaud, a Democrat, has been elected to the U.S. House five times in the 2nd District. His Republican challenger this fall, Maine Senate President Kevin Raye, cites internal polls showing him trailing Michaud by less than 10 points.

But public polling in the race has given the Democratic incumbent comfortable, double-digit leads. Ben Grant, who heads the Maine Democratic Party, says Romney's allies are wasting their money in Maine.

"I think this far too little, too late," he says. "I think the polling, both nationally and here in Maine, shows that there aren't a lot of undecided voters left. I'm partly kind of happy they're spending money here because that's $300,000 they're not spending someplace else, where they might actually have a shot."

Romney's chances in the 2nd District are open to debate. What's more certain, says Dan Shea, is what Restore Our Future's ad spending in Maine says about the overall state of the presidential race. Shea is professor of government at Colby College, where he also runs the Goldfarb Center for Public Affairs and Civic Engagement.

"When operatives make moves like this, it really reinforces what we're starting to learn: They've got their finger on a lot of information, a lot of polling data. If they're investing hundreds of thousands of dollars in the 2nd District in Maine, that means it's very tight nationally," Shea says.

Consider this scenario: President Obama wins Wisconsin, Virginia, New Hampshire and Nevada. Mitt Romney wins Florida, North Carolina, Ohio, Colorado and Iowa and Maine's 2nd Congressional District, producing a 269-269 tie in the electoral college and sending the deadlocked race to the new House of Representatives.

With the House likely to remain in Republican hands, it would almost certainly vote to make Mitt Romney the next president of the United States.