President Obama thinks he knows the key to re-election, and it's very close to the White House.

Right across the Potomac River, in fact, in Virginia.

"If we win Virginia, we will win this election," Obama told supporters last night at a high school in Leesburg, Va.

Four years ago, Obama became the first Democratic presidential candidate to win Virginia since President Lyndon Johnson in 1964. (He also won neighboring North Carolina, the first Democrat to do so since Jimmy Carter in 1976.)

This year's race in Virgina features a wild card: a potential independent candidacy by former U.S. congressman Virgil Goode, a Virgina resident.

A former Democrat-turned-Republican, Goode is a conservative and could take a significant number of votes from Republican candidate Mitt Romney.

Republicans from Ronald Reagan to George W. Bush made Virginia a cornerstone of a solid GOP South in presidential elections.

Obama's cracking of the South virtually guaranteed his win over John McCain, and would probably do so again against Romney.

The Republicans know this as well, which is why Romney plans to spend a lot of time in Virginia.

For Obama, the key to Virgina is the northern part of the state, the growing suburbs around Washington, D.C., which are increasingly Democratic.

That includes Loudon County High School, where Obama spoke last night.

"If you still believe in me like I believe in you, I'm asking you to stand with me," Obama said. "You got to make some phone calls with me, knock on some doors for me, recruit your friends and your neighbors with me."

"We won Loudoun County last time," he added. "And if we win Loudoun County this time, we will win Virginia. And if we win Virginia, we will win this election."