Polls close at 8 p.m. Eastern time in Florida, Pennsylvania and Missouri, three of the most important presidential battlegrounds. Polls have shown Missouri and Florida to be tossups and Sen. Barack Obama (D-Ill.) leading consistently in Pennsylvania. Sen. John McCain (R-Ariz.) may have to win Missouri and Florida to stay in the race. If he takes Pennsylvania, it could signal a very close race. McCain and GOP vice presidential candidate Gov. Sarah Palin of Alaska campaigned aggressively in Pennsylvania in the final weeks of the campaign, hoping to seize from Obama a state that voted Democratic in both 2000 and 2004.

With memories perhaps still fresh of misleading early exit polls in 2004 that predicted a victory for Sen. John Kerry (D-Mass.) — not to mention the mistaken early call of the presidential election in 2000 —networks were generally being conservative in calling states for either Obama or McCain, choosing to wait until enough actual votes are counted before making a selection. As this was filed, CBS had called one key battleground state — saying McCain would take West Virginia. At one point viewed as nearly a tossup, West Virginia had moved a little more firmly into McCain’s column in recent polls.