Consider that as of Tuesday afternoon, President Obama’s lead in the RealClearPolitics average of national polls was 1.3 percentage points over Mitt Romney.
But Mr. Obama led by a mean of 3.5 points in the RealClearPolitics averages for the 10 states (Ohio, Virginia, Florida, Pennsylvania, Colorado, Iowa, Nevada, Michigan, New Hampshire and Wisconsin) that are most likely to determine the election outcome, according to our “tipping point index.” If the list is expanded to cover the five other marginally competitive states where RealClearPolitics calculates a polling average — Arizona, Minnesota, Missouri, New Mexico and North Carolina — Mr. Obama’s lead averages 3.1 points, according to the numbers.
While that isn’t an enormous difference in an absolute sense, it is a consequential one. A one- or two-point lead for Mr. Obama, as in the national polls, would make him barely better than a tossup to win re-election. A three- or four-point lead, as in the state polls, is obviously no guarantee given the troubles in the economy, but it is a more substantive advantage.