“Just be patient,” some North Carolina Democrats are telling each other.

“The demographics,” they say, “are on our side. The older white conservative Republicans are dying off. They are being replaced by younger, multi-ethnic, social liberals who tilt Democratic when they go to the polls. It is just a matter of time until these factors give the edge in North Carolina politics back to the Democrats.”

Before Democrats celebrate their coming return to power, they must deal with another set of factors outlined by Nate Cohn in recent articles in The New York Times.

Cohn explains why President Obama’s landslide victory in 2008 has not led to a new national Democratic era as many predicted.

“Six years later,” he writes, “there is not even a clear Democratic majority in the country, let alone one poised for 30 years of dominance.”

Cohn concedes that Obama’s 2008 coalition of young and nonwhite voters again turned out in record numbers in 2012. But something else is happening, he says.

“The Democratic majority has failed to materialize because the Republicans made large, countervailing and unappreciated gains of their own among white Southerners. From the high plains of West Texas to the Atlantic Coast of Georgia, white voters opposed Mr. Obama’s re-election in overwhelming numbers. In many counties 90 percent of white voters chose Mitt Romney, nearly the reversal of the margin by which black voters supported Mr. Obama.”

Cohn is more disturbing when he concludes, “Southern politics are deeply polarized along racial lines. It is no exaggeration to suggest that in these states the Democrats have become the party of African Americans and that the Republicans are the party of whites.”

Although Cohn acknowledges that some “metropolitan enclaves” in North Carolina, Virginia, and Florida have been transformed into liberal bastions, he says, “much of the South remains largely untouched.”

While young voters in the rest of the country have moved to the left on issues like gay marriage and immigration, Cohn says, “young Southern whites are just as conservative as their parents and grandparents. If they remain so, the gap between the South and the rest of the country could grow further.”

At the national level there is an upside for Democrats from the Republicans’ success in the South. Cohn explains it this way: “Whatever is causing Republicans to excel in the South, whether religion or race, just isn’t helping them elsewhere.”

As the South becomes more Republican, our region increasingly imposes its character on the party, which as Cohn says, makes broadening its national appeal more challenging.

For instance, any moderate Republican presidential candidate “would struggle to win Southern primaries, where many voters adhere to conservative orthodoxy. The road to the nomination without the South, which holds such a large share of the party’s elected officials and voters, is narrow and long.”

What does all this mean for the reelection prospects for U.S. Senator Kay Hagan? Cohn says she has a special challenge and is “far more vulnerable than she appears at first glance. North Carolina might be the state where Democrats suffer the most from low midterm turnout. The state is divided between older, culturally Southern and conservative voters, and younger, more diverse and more liberal voters, especially around the Research Triangle and Charlotte.

“In presidential elections, those two groups fight nearly to a draw. In midterm elections, when older voters turn out at much higher rates than younger ones, the Republicans have a big advantage.

“If Ms. Hagan cannot broaden her political appeal, it is not clear she can win a midterm election in North Carolina.”

As a moderate woman with experience as campaigner, fundraiser, and senator, Hagan has the ingredients to broaden her appeal and put together a successful campaign, notwithstanding the challenges Cohn has laid out for her and other North Carolina Democrats.