Get out your calculator. In one sense, Electoral College math is simple: Add up states’ electoral votes until one presidential candidate’s total is 270 or greater. In another sense, it is complex because there are many ways for each candidate to achieve that sum -- and even some ways for neither to reach 270.
Based on polling data aggregated by the website RealClearPolitics, President Obama has 201 electoral votes safely in the bank. Republican challenger Mitt Romney has 191.
The remaining 146 electoral votes are spread among 11 battleground states where recent polling averages show the candidates separated by fewer than 5 percentage points. It is here that the election will be decided.
Obama leads nine of these states while Romney leads only two. If the election were to play out as recent survey averages suggest, Obama would win reelection, 303-235.
But Romney could walk a very short path to the White House by claiming the biggest battleground prizes. With 29 electoral votes from Florida, which Romney leads; 20 from Pennsylvania, where he has made a late run; and 18 from Ohio, the GOP nominee would have 258 electoral votes and need to win only one more -- Michigan (16 votes), North Carolina (15) or Virginia (13). Romney could win just four of 11 swing states and claim the presidency.
If Romney fails to pull off an upset in Pennsylvania, where he has not led a major poll since February, his chances remain decent. The key would be to win Florida, North Carolina and Virginia -- the three swing states where he is strongest -- and to take Ohio, without which no Republican has ever won a presidential election. Those four states would give Romney 266 electoral votes. At that point, even tiny New Hampshire, with four votes, would be enough to give Romney 270.
Without Ohio, Romney’s prospects dim. Florida, North Carolina and Virginia leave Romney with 248 electoral votes and a lot of work to do. He could win New Hampshire, Iowa and Colorado -- giving him a majority of the swing states -- and still come up short.
If Obama wins Florida, Pennsylvania and Ohio, he would have 268 electoral votes and need only one other state to secure reelection.
Obama also could hold on to the White House without Florida by winning just the five swing states where his leads are the widest: Wisconsin, Michigan, Pennsylvania, Ohio and Nevada.
The president could even lose four of the six biggest states -- Florida, Ohio, North Carolina and Virginia -- and still win reelection by claiming Pennsylvania, Michigan and all of the smaller swing states.
It is possible for Obama and Romney to tie at 269 electoral votes apiece. Romney wins in Florida, Ohio, North Carolina and Wisconsin -- the home state of his running mate, Paul Ryan --would give the Republican ticket 263 votes, and a victory in either Iowa or Nevada would push Romney to 269.
Romney could also win Florida, Ohio, North Carolina, Virginia and New Hampshire but wind up with 269 votes, instead of 270, if Obama won the Omaha congressional district in Nebraska, as he did in 2008. Nebraska is one of only two states to award its electoral votes by congressional district, instead of on a winner-take-all basis.