Late on election night, a small melee erupted at the University of Mississippi here when a group of white students frustrated by the reelection of President Obama marched outside and began shouting racial slurs at African American students. Several hundred people gathered to watch as two white students were arrested.

“Mississippi still has a lot of work to do in race relations,” said Kimbrely Dandridge, an African American Obama supporter and president of the student body.

Yet even as that incident evoked ugly memories of an earlier era, Election Day in the South told a newer and more surprising story: The nation’s first black president finished more strongly in the region than any other Democratic nominee in three decades, underscoring a fresh challenge for Republicans who rely on Southern whites as their base of national support.

Obama won Virginia and Florida and narrowly missed victory in North Carolina. But he also polled as well in Georgia as any Democrat since Jimmy Carter, grabbed 44 percent of the vote in deep-red South Carolina and just under that in Mississippi — despite doing no substantive campaigning in any of those states.

Much of the post-election analysis has focused on the demographic crisis facing Republicans among Hispanic voters, particularly in Texas. But the results across other parts of the South, where Latinos remain a single-digit minority, point to separate trends among blacks and whites that may also have big implications for the GOP’s future.

A look at key factors in the 2012 presidential election.

The results show a region cleaving apart along new electoral fault lines. In the region’s center, clustered along the Mississippi River — where Bill Clinton polled most strongly — the GOP remains largely unchallenged and the voting divide between blacks and whites is deepening. Nearly nine of 10 of white voters in Mississippi, for instance, went for Republican nominee Mitt Romney this year, according to exit polls. About 96 percent of black voters in the state supported Obama.

The pattern is markedly different in the five states that hug the Atlantic coast from Virginia to Florida, which together hold 82 of the South’s 160 electoral votes. A combination of a growing black population, urban expansion, oceanfront development and in-migration from other regions has opened up increasing opportunities for Democrats in those states.

“Georgia is an achievable target for Democrats in 2016,” said Atlanta Mayor Kasim Reed, a frequent Obama surrogate during the campaign. “What you’re going to see is the Democratic Party making a drive through the geography from Virginia to Florida.”

That will be easier said than done — particularly when the Democratic nominee is not Obama — but powerful forces in the region are clearly eroding GOP dominance. The trends pose difficulties for a Republican Party that has been shifting toward Dixie since the “Southern strategy” of the Nixon era, which sought to encourage white flight from the Democratic Party.

In every Southern state except Louisiana, the population of African Americans grew substantially faster than that of whites over the past decade. The growth is fueled by black retirees from the north and rising numbers of young, well-educated blacks in prosperous cities such as Atlanta, Norfolk, Charlotte and Charleston, S.C.

The influx also includes fast-growing, but smaller, Hispanic populations and an infusion of less-conservative outsiders attracted to popular coastal areas. Together, the shifts are making the electoral landscape from Virginia and the Carolinas look increasingly like the swing state of Florida.

Obama’s 2012 numbers in the Southeastern coastal states outperformed every Democratic nominee since Carter and significantly narrowed past gaps between Democratic and Republican candidates. The lone possible exception is Georgia in 1996, which gave Arkansas native Bill Clinton 45.8 percent in 1996; Obama fell 0.4 percent short of that mark in tentative 2012 results, but ongoing revisions could close the gap.

The proportion of white voters in the South is also shrinking. Southern whites voted overwhelmingly for Romney, but in six Southern states, far fewer of them appear to have gone to the polls on Nov. 6 than the number who voted for Sen. John McCain (R-Ariz.) in 2008.

In Florida, the share of votes cast by whites this year fell to 66 percent, down from 73 percent in 2000. In Georgia, the number of white voters declined while African American registration increased nearly 6 percent and Hispanic voters grew by 36 percent.

“Republicans can focus all they want on Hispanics,” said John Anzalone, a Montgomery, Ala., pollster who helped analyze swing states for the Obama campaign. “But they also have a problem with whites, in this election cycle, just showing up.”

Many Republican leaders in the South say the lower turnout by whites in some areas simply reflected lower enthusiasm for Romney as a candidate, and doesn’t signal a longer term decline in GOP strength.

Prominent conservatives in the region are acutely aware of the danger posed by the trends. “We’ve got to go out and sell our ideas not just to the choir, but the whole church,” said Henry Barbour, a Republican National Committee member from Mississippi and a top Romney fundraiser (and nephew of former governor Haley Barbour). “We’re not going to get 25 percent of the black vote in four years, but we’ve got to figure out which African Americans share our core beliefs.”

Some Republicans had hoped to make at least small inroads among black voters in 2012 given lower African American turnout in the 2010 midterms, high black unemployment and the modest success of presidential candidate Herman Cain in the Republican primaries. They reasoned that winning over just a small percentage of black voters in key states such as Virginia, North Carolina and Florida could alter the outcome of the race.

The Rev. C.L. Bryant, an African American tea party activist from DeSoto Parish, La., helped lead a spirited effort by some of the most conservative GOP-aligned groups to use Obama’s support for gay marriage as an opening to appeal to socially conservative black voters.

He produced a feature-length film titled “Runaway Slave” that urged blacks to flee the Democratic Party. It was shown in more than 20 cities, while he and other conservative African Americans toured the country to blast Obama’s support for abortion rights and gay issues.

But the issues had little apparent impact on Obama’s support within the black community. Black pastors — some of whom had preached against gay marriage in the past — rallied to the president. Romney also hit a number of sour notes with minorities during the campaign, including his apparent suggestion that blacks who support Obama want “more free stuff” from government.

“Romney was real disrespectful,” said Rodney Collier, 58, a black stylist at Haywood’s Hair Images in Richmond. “How can you be so negative and nasty to a sitting president?”

By the closing stage of the campaign, gay marriage had largely disappeared from the conversation among black voters. “We don’t see any of that,” said Tiara Moore, 23, a biology student, after a day of canvassing before the election at historically black Hampton University in Virginia. “They talk about health care and student loans.”

Contrary to the expectations of many Republican pollsters, black voters came out in droves on Election Day and voted overwhelmingly for Obama — near or above 95 percent in most parts of the South.

“We were all basically stunned at the results,” Bryant said. “It is very clear that the direction of the Republican Party — the conservative movement — is necessarily going to have to include the changing face of America and address the concerns of minorities, blacks, Latinos, and even younger white women, all young people. . . . It has to happen or we’re going to be insignificant.”

Danielle Fisher contributed to this report.