Thirteen days. The final countdown. Barring an external event of significant proportion, not much will change to affect the outcome. And it’s now all a turnout game.

Forget the national polls showing President Barack Obama and Governor Mitt Romney in a dead heat or a statistical tie in the race for the White House.

In 2012, the road to 1600 Pennsylvania Avenue runs through one state: Ohio.

According to Real Clear Politics, Romney leads Obama 206 to 201 in possible electoral votes, based on the averages of polling by state. That leaves 131 still up for grabs. Do the math. The challenger needs 64 or more, and the incumbent, 69 or more, to get to the magic number of 270. (Assuming it does not end in a tie.)

The RCP toss-up states and their electoral votes are: Colorado (9), Florida (29), Iowa (6), Michigan (16), Nevada (6), New Hampshire (4), Ohio (18), Pennsylvania (20), Virginia (13), and Wisconsin (10).

Not so coincidentally, both candidates are on a whirlwind tour visiting many of those states this week. While there are several numerical pathways to electoral victory for either man, the math is harder for Romney without Ohio.

Trite but true: As Ohio goes, so goes the nation.

Ohio has voted for the winner in every presidential election since 1964. No Republican has ever won without carrying the state; only two Democrats in the last century have won without Ohio.

George W. Bush won Ohio in 2004 by 118,601 votes. Obama won by just 262,224 votes, despite a larger share nationally.

With every vote needing to count, no wonder the president and vice president have visited the Buckeye State 10 times in the last 30 days, and have reportedly poured $57 million into broadcast ads there. Romney and Ryan have been there 21 times, spending $34 million on ads.

And right now, Obama is ahead.

The president is likely to win women in Ohio, and 275,000 more women than men voted in 2008. He is also likely to hold his support among young, black, and Hispanic voters, but they are not the majority in the state.

Romney’s double-digit lead among white voters nationally, the largest demographic segment of the electorate, should help him in Ohio. But many Ohioans are blue-collar, industrial workers. One-in-eight jobs are auto-related. And Obama’s attacks on Romney’s position on the auto bailouts are likely resonating.

As of Tuesday, more than 1.6 million of Ohio’s 7.9 million registered voters already have cast a ballot or have requested an absentee ballot. And surveys show Obama is winning the majority of the early votes, by as much as a two-to-one margin.

With 13 days to go, the ground game matters.

Team Obama remains confident in the favorable demographics of new registrants, in their share of early voting, and in their ground game in Ohio leading to Nov. 6. Team Romney has a lot of ground to catch up to get his supporters out on or before Election Day.

While voter enthusiasm is higher among GOP voters than Democrats, fear is also a great driver. But which fear is greater? Democrats fear of Romney winning? Or Republicans fear of four more years of Obama?