It's a horserace now. While there is only one poll that matters: November 6th, the Real Clear Politics aggregate of polls shows neither candidate having more than 50% of the vote in enough states to win the election, as of today. While their National polling aggregate shows Romney ahead by 1.4%, he still doesn't have more than 50% of the vote.
Some States are not even in contention, and won't ever be, unless something dramatic changes. The combined vote of CA, NY, IL, 7 others will always outweigh that of Middle America's farmers & factory workers. In fact, the 17 states the Democratic candidate can almost always count on in every election mean the party only needs to find another 69 electoral votes. That's why both campaigns are so focused on Ohio. It will likely decide the election. In all liklihood, the majority of States will likely vote for Romney, but the majority of those living in big cities, like New York City, San Francisco, and Los Angeles will vote for Obama. I doubt anyone has trusted the published results of Chicago since the mafia delivered the union vote for JFK in 1960. The cemetary vote is very powerful there. And the urban District of Columbia has a unrepresentatively powerful 3 electoral votes that will always go into the DNC category.
One of the great features of Real Clear Politics is that you can change the electoral vote, or at least how you think it'll shake out. Another reason, I look at it, is that it aggregates several polls, so it is probably more accurate. And we're getting close enough, that it actually could be predictive of the final results. It predicts a very tight race. In a no toss-up vote, it shows Obama winning, but when the margin of error is factored in, it can also predict a Romney win. At present, the difference hinges on margins as thin as 1.7% in Ohio and 0.4% in Virginia. Both States have a Margin of Error of greater than 3%, including some old polls, and neither State has polls showing an absolute majority in either candidates favor. In fact 11 States representing 146 electoral votes show majorities of less than 50%.
In the map to the right, the darkest shades represent those States that are solidly DNC or RNC, while the lightest shades could end up in either column. It shows a likely scenario in which Romney would win. All of the light blue and pink states have polls without a 50% majority for either candidate. Three of those States' have polls under 1% simple majorities, and 2 under 2%. To win, Obama only needs to change the electoral vote for one of those shown above to light blue. Currently, Ohio is polling at 1.7% for Obama, but that shows a significant momentum swing against him.
In the map to the left, the majority of America has still voted for Romney, but the extremes of America, the West Coast and the Northeast's electoral DNC loyalty, mean that Obama only needs to convince a few more people in Cincinnati, Dayton, and Toledo to vote for the incumbent.
There are other scenarios which would produce an Obama win, or a Romney win, but this is where both politicians are focusing their main efforts. It's not that a Republican has never won without Ohio. It's that since the reversal of poltical polls that occured in the elections of Reagan, no Republican has been able to overcome the guaranteed votes of NY and CA without Ohio.
The other point that could be made is that the blue States in the map are Union States, not as in the Civil War, but as in the Labor scenario. Though the Unions have weakened in membership in recent years, their political loyalties and campaigning have increased. The red States are more likely to have a "Right to Work" law, i.e. a law stating that an employee cannot be compelled to become a Union Member in order to gain employment. The corporate employment agencies, known as Unions, then siphon off considerable wages from those employees, and in turn send out what amounts to campaign literature for the DNC, and campaign funds to it. They organize rallies, regardless of voting district, or state, even paying non-Union members to hold signs and shout.
The question is not if Romney and Obama will spend enough money in Ohio to turn out the vote, but if the ads will turn the voters off to the point that Ohioians will decide not to vote. But Ohio seems to care more about the debates, than the ads. At present, the polls show Romney winning the popular vote while Obama wins the electoral vote, in a razor close election. There are even scenarios where the vote gets sent to the House of Representatives to make the final decision. For example, if Virginia, Nevada, and Iowa go to Romney and Ohio goes to Obama, then each could end up with 269 electoral votes, and the House of Representatives would be tasked to break the tie.
While a vote in Illinois or California may not have much weight this year, or any year, this election could quite easily rest on a recount and single vote in Ohio, and or Virginia, or a few other States.