While President Obama’s lead in Ohio is not large, most polls show he is winning. The latest SurveyUSA poll finds Obama with a three point lead over Mitt Romney.

Ohio
SurveyUSA (10/12-15)
Barack Obama 45%
Mitt Romney 42%
Other 3%
Undecided 9%

Beyond still holding a narrow lead, the reason the Obama campaign seems to view Ohio as their firewall is that they have already managed to bank an impressive advantage in the early voting. According to the SurveyUSA poll, roughly one fifth of the electorate has already cast their votes in Ohio. Among those who have already voted, Obama is winning 57 percent to 38 percent. To close a three point gap in overall polling Romney would need roughly a four point swing in his direction in those who have yet to vote. Everyday the number of people who could theoretically change their votes in Ohio shrinks.

If Obama can win Ohio’s 18 electoral votes he will dramatically reduce Romney’s potential paths to the necessary 270 Electoral College votes needed to win the presidency. Thanks to polls showing a tight race in Wisconsin and Virginia, the possibility of Romney winning without Ohio has become more plausible but it would still be extremely difficult.