In Florida, for example, Obama defeated Romney by 46,000 votes; meanwhile, Ron Paul received over 117,000 votes in the primary. If only 40% of these Ron Paul Republicans stayed home on Election Day, it would have been enough to cost Romney the state and its 29 electoral votes.
A similar case can be made for Connecticut, New Hampshire, Ohio, and Virginia. Along with Florida, these five states account for a whopping 71 Electoral College votes. Remember that Obama earned 332 electoral votes compared to Romney’s 206. Had Romney won these five states, they would have been sufficient to give him a narrow 277-261 victory over the President."