President Barack Obama almost ran the table Tuesday night when it came to battleground states.

The lone exception: North Carolina.

Of a dozen competitive states, it was the only one that went from Democratic blue in 2008 to Republican red this year.

Why didn’t Obama carry the Tar Heel State?

Here are five reasons:

1. The sour economy

During the 2008 campaign, at the outset of the recession, then-Sen. Obama blamed the economic collapse on Republicans. That argument helped make him the first Democratic presidential candidate to carry North Carolina since Jimmy Carter in 1976.

But even under those optimal political conditions, Obama won this traditionally Republican state by less than one percentage point. It was his narrowest victory in 2008.

So President Obama had little N.C. cushion going into the 2012 campaign. And this time, Republicans were blaming him for the state’s 9.6 percent unemployment rate, the fifth highest in the country.

At least two other battleground states were also suffering economically in this election year. But Obama had carried Florida by nearly 3 percentage points in 2008 (he is slightly ahead there in the latest vote totals), and his margin in Nevada was more than 12 percentage points four years ago.

“Obama only won it here by 14,000 votes last time and we knew this election would be closer,” said Andrew Taylor, a political scientist at N.C. State University. “So, with the (bad) economy and the slight movement toward the GOP, everybody knew that North Carolina would be this low-hanging fruit (for the GOP) – the first state to go.”

Taylor and others are only surprised that Obama didn’t lose the state by more than 97,000 votes.

2. GOP honed ground game

In 2008, Obama’s North Carolina campaign caught GOP Sen. John McCain’s campaign napping. By getting so many of their voters – mostly African-Americans, young people and women – to the polls during early voting, the Obama forces were able to build up a 305,000 vote advantage going into Election Day.

This year, Republicans were wide awake. Romney got 95,000 more early North Carolina votes than McCain did in 2008. Obama, meanwhile, got 39,000 fewer than four years ago.

Going into Tuesday, Obama was leading by 207,000 votes – not enough, as it turned out, to overcome Romney’s Election Day voting advantage.

Put another way: The Republicans “shaved almost 100,000 votes off” Obama’s 2008 early vote margin, said Catawba College political scientist Michael Bitzer.

For a closer look at the effect of a stepped-up GOP effort, consider Watauga County, a bellwether for North Carolina that went with Obama in 2008 but for Romney on Tuesday.

Watauga is home to Appalachian State University. And one of the differences between 2008 and this year was an increased effort by College Republicans on the campus, said App State political scientist Phillip Ardoin.

“The College Republicans were much more effective, much more engaged than in 2008,” he said.

Romney’s victory margin in Watauga: 753 votes.

3. A slip in urban margins

Four years ago, Obama’s big victory margins in several of North Carolina’s urban counties were enough to overcome lopsided defeats in many smaller, rural counties.

This year, those margins shrunk in a few key counties.

Obama won Wake County by 64,000 votes four years ago. On Tuesday, he won by 54,000.