Nate Cohn examines both candidates' paths to victory in Ohio. One reason Obama is ahead:

Obama’s road to victory in Ohio starts with a strong showing among the African American voters that provided Bush with reelection eight years ago. It’s often overlooked just how much Obama gains over Kerry’s performance just by winning an outsized share of African Americans. According to the 2004 exit polls, Bush’s concerted efforts to appeal to African American voters—mainly on cultural issues—held Kerry to just 84 percent of the black vote. African American voters predictably swung decisively toward Obama, offering him 97 percent of the vote on Election Day with an additional point of black turnout.

In 2004, Bush won Ohio by 118,000 votes, but Obama’s gains among African American voters are sufficient to erase Kerry’s deficit without any changes in the composition of the electorate. 

Alex Roarty reviews recount rules:

Ohio orders a recount if the margin between the top two candidates is within one-fourth of a percentage point of the total votes cast.

But such a recount would begin only after the election results are certified in each individual county — and the deadline for that is 21 days after Nov. 6. The secretary of state would then need to certify the results, which a spokesman indicated would take a few additional days. In other words, it could take until December before a recount in Ohio even begins.

Candidates can also request a recount in Ohio, either for the entire state or individual precincts.