Obama holds slight electoral vote edge, according to new computer simulation

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By Anthony Salvanto and Doug Rivers

President Obama would hold a slight Electoral College edge if the election were today, according to a new computer simulation model, mainly because enough of the battlegrounds still tilt ever-so-slightly his way -- but he's not nearly favored for re-election to the extent he was a few weeks ago.

CBS News and YouGov's simulation shows how the national presidential vote impacts the Electoral College, following Mitt Romney's resurgence and the first debate.

We tested what would happen in the Electoral College under three very close national vote scenarios: either a slight Obama or Romney popular vote win, and a tie. The model shows us how the nation's votes would be distributed in each case, and how the states would ultimately tip one way or the other. (We tried all three scenarios because if there's one thing - and maybe the only thing - that the national polls agree on today, it's that this race is close.)

If the popular vote is tied

A tie in the national popular vote means Mr. Obama would likely get re-elected narrowly with 290 electoral votes--just over the 270 needed to win.

The president can simply tie the popular vote and still win the Electoral College because he has more state-by-state combinations to get to 270 than Romney does. So he'd most likely squeak out wins in most of the battlegrounds where he leads - enough for that 290 majority - while losing a few others, and breaking even in the popular vote. He'd rely heavily on slight wins in Ohio and smaller states like Colorado and Iowa and Wisconsin to get him there, because Romney would take larger prizes of Florida and Virginia by very small margins, as well as North Carolina.

However, this would be a razor-tight race all around: less than one percent would separate the candidates in five battleground states (Ohio, Wisconsin, Iowa, Colorado and Virginia). All told, the model shows a 65 percent chance of Mr. Obama winning in a tied popular vote scenario. And Romney is within electoral striking distance, too, because he'd likely win the big prize of Florida under this and most of the scenarios we examined. That alone gets him much closer to 270 and ups his chances.

Before we look at the other scenarios, here's more detail on how the model works: First, we estimate where the race stands at this moment in both battleground and non-battleground states using YouGov's interviews with 35,700 registered voters across the country, conducted for this project. Then, since the national vote is really just an assemblage of state votes, we look at how the states are likely to tip from their initial position as we see shifts in the national vote. We used one million computer simulations to estimate the chances of each possible Electoral College combination that could result, and from that we learn which are the most likely to occur.

Importantly, it is meant to gives us a snapshot of today, not a prediction, because it is based on current information and the current dynamics of the race.