According to Leip's swing data for 2008, voters swung to the Democratic Party by 9.73%. The below scenario assumes a half-back swing; 4.86%. The 4.86% has been distributed evenly, subtracted from Obama and added to the Republican in all 50 state + D.C. As you can see, that produces a very tight election.
Republican:280
Democrat:258
States with a 1% Margin
Colorado
Iowa
Minnesota
Pennsylvania
New Hampshire
If you subtract 4.86 points to Obama and give them to the GOP candidate, this produces a 9.72 swing toward the GOP. In order to have a "half-back swing", you need to substract only 2.43 points.
