See also US Elections Analysis: Obama Wins, But Romney Stakes Claim to Be Commander-in-Chief
In our latest 6-minute guide on How to Become an Expert on the US Presidential Election, we explain why the race is now down to "Ohio+4".
If Mitt Romney takes Ohio, then he needs to win at least two of these four states --- Virginia, Colorado, Iowa, and Nevada --- to move into the White House.
But if Romney loses Ohio, then he has to win all four of those states for a 269-269 tie in the Electoral College, taking the decision to the House of Representatives.