Mitt Romney doesn’t need to win Ohio to win the presidential election, he needs to do well enough overall that he ends up winning Ohio. There’s a huge difference.
First, remember that correlation is not causation. Ohio voters do not cause voters in other states to vote one way or another, such that securing Ohio votes secures votes in other states. Ohio reflects a larger trend.
The Electoral College scenarios by which Romney can win the election start to proliferate at the point where he’s doing so well generally that the most likely outcomes include him snagging Ohio. The site 270ToWin  reports that there are 161 combinations of swing states Romney can win to reach 270 electoral votes, but that 8 out of the 10  most probable ways involve winning Ohio. Nonetheless, Romney should concentrate on doing well generally, not spending all his time in Ohio.
Second, it’s true that since the first election in which Republicans participated in 1856, the party has won Ohio every time it has won the White House. However, since 1928 the same statistic is true  for Colorado, Florida, Nevada, and Virginia, all swing states this election cycle. That is, 100% of the time the GOP won the White House since 1928, it also won each of these states. (North Carolina and New Hampshire also have near-perfect records on this metric.) So why the obsessive focus on Ohio?
Also consider the inverse question: When the Republican lost the White House, how often did he lose particular states? Since 1928, Republicans who lost the White House lost Ohio 82% of the time. But they also lost Florida, Pennsylvania, and North Carolina  82% of the time, and Nevada 91% of the time. Again, why the spotlight on Ohio?
Here’s the real reason Ohio keeps getting so much national attention: luck.
For 75 years after the Civil War, Ohio was a much more Republican state  than it is today. Thus, it’s not surprising that Ohio had a perfect record predicting Republican wins during that period.
Then Ohio went for Roosevelt in 1932, 1936, and 1940, during the Great Depression. Since then, shifting demographics—an influx of Democratic-voting African-Americans from the South, a trend for Ohio unions to become more Democratic under FDR—morphed Ohio into its present-day, racially-mixed, blue-collar, purple condition .
After 75 years of being solidly Republican, another 75 years of good luck as a swing state in predicting elections—but no better than Florida, Virginia, Colorado, or Nevada—gave Ohio the bellwether reputation it has today.
But none of those swing states was as consistently Republican  as Ohio in the 75 years prior to 1928. This explains why none of their track records goes as far back as Ohio’s in picking Republicans, and why no one cites these as bellwether states today. Specifically, Ohio voted for the Republican candidate 89% of the time  in elections between 1856 and 1924, compared to only 60% for Nevada, 58% for Colorado, 18% for Florida, and 6% for Virginia.
Saying that Ohio was a bellwether state for Republicans from 1856 to 1924 is like saying that Kansas was a bellwether state for Republicans during that period. Imagine if Kansas’s demographics had suddenly shifted during the Great Depression, such that a greater proportion of likely Democratic voters began flooding the state, and Kansas suddenly become a swing state. Then everyone would be proclaiming today that no Republican president has ever won the White House without winning Kansas.
In short, for 75 years Ohio was Kansas, then it turned purple and had a string of good luck predicting elections for 75 years (like Florida, Virginia, Colorado, Nevada, North Carolina, and New Hampshire); ergo, pundits consider Ohio an infallible barometer of the national political soul back to the days of Abraham Lincoln.
The Ohio effect is a historical anomaly, and any of a number of other states could easily replace it as a more accurate bellwether as we experience changing demographics, population shifts, and voting trends in years to come. The fact that the Ohio vote will likely depend on just a handful of on-the-fence counties —not a statewide electorate wildly shifting back and forth from election to election—reinforces this notion, as does the fact that Ohio’s electoral count has been dwindling  since 1968.
Ohio is the Republican bellwether state—until it isn’t. One of these days, a Republican is going to win the general election without taking Ohio, and it could happen in 2012. Pundits will simply move the starting date of their favorite metric to the earliest date after which one of the other swing states had a perfect record, then declare this new state the hurdle Republicans absolutely must clear to win the general election.
Instead of camping out in Ohio for the next week, Romney should focus on connecting with as many voters in all of the swing states as possible, and hope that his nationwide momentum spreads to the important, but not eternally-important, Ohio.
Previously published in modified form at Red Alert Politics