The latest Washington Post-ABC News poll highlighted just how much the coalitions of the two political parties have changed over time and continue to shift during Barack Obama’s presidency. What advisers to the president and Mitt Romney are trying to calculate is how that may affect the electoral college.

The poll’s results were not truly surprising, but they captured something that reflects current social realities. The survey found that the most economically stressed white voters in this country view Mitt Romney far more favorably than the president when it comes to handling the economy.

A labor official e-mailed me the day the story by my colleagues Karen Tumulty and Jon Cohen appeared, saying: “A Democratic president is losing the jobless. . . . FDR must be spinning in his grave.”

The truth is that Democratic presidential candidates have been losing among white voters, particularly those without college degrees, for years. Obama wasn’t the first, but he has clearly struggled as much as, or more than, any of his predecessors in attracting support from that group.

That fact was underscored by Democratic primaries in Kentucky and Arkansas last week. Obama lost roughly 40 percent of the Democratic vote in essentially uncontested events, just as he had in Oklahoma earlier in the year. Although those results drew attention and commentary, they, too, were hardly a surprise.

Four years ago, Obama was wiped out in those states during his nomination battle against Hillary Rodham Clinton. In the general election, he fared worse than the 2004 Democratic nominee, John F. Kerry, did in an arc of heavily white counties running south and west from West Virginia through Arkansas to Oklahoma, even though virtually all other counties in the country gave him a higher percentage of the vote than the Democrats got in 2004. The disaffection with Obama among voters in those counties is no doubt mostly cultural, although race probably plays a role as well.

Another aspect of these shifts is more important: Obama is winning a declining share of what is a steadily declining share of the electorate. In the long run, the changing electorate is a far bigger problem for Republicans, who remain overwhelmingly white in their makeup.

The coalition that Obama began to assemble in his first campaign and continues to focus on in his reelection bid depends less on maintaining his share of the white working-class vote and more on maximizing his support among the rising share of the electorate accounted for by minorities. The shifting balance is well known and closely tracked by Obama loyalists — both the national trends and the changes in the handful of states where the election will be decided.

The macro numbers, set out over time, tell the story graphically. When Bill Clinton was reelected in 1996, white voters made up 83 percent of the electorate. When Obama was elected four years ago, they accounted for just 74 percent. This fall, whites may make up only 72 percent of the vote.

Where he is weakest, of course, is with white voters who were once core members of the Democratic coalition, working-class Americans whose support was consolidated by Franklin D. Roosevelt’s New Deal and who formed the backbone of both the nation’s economy and the Democratic Party for years. Today, those voters — generally whites without college degrees — tilt Republican.

That could be problematic for Obama in at least a few of the battleground states in the industrial Midwest. William Frey of the Brookings Institution, a leading demographer who closely tracks changes in the population, noted that in some of those Midwest states, older white workers without college degrees are actually a rising share of the population. In Ohio, for example, the percentage of whites ages 18 to 64 without college degrees was 54 percent in the latest census, a point higher than it was previously.

One thing that is important to remember is that despite his poor performance among white working-class voters in the 2008 primaries in Pennsylvania and Ohio, Obama came back to win both states in the general election.

The president cannot afford a true collapse in white working-class support, but it’s possible he can overcome some further slippage if he is as successful this time in drawing sizable numbers of African Americans, Hispanics and other minorities to the polls — and if he can continue to build support among whites with college degrees.

That’s not yet guaranteed, although the ingredients are there for him to continue to remake the party’s coalition. But three states where Obama and Romney will be battling this fall — Florida, Nevada and North Carolina — offer insights into how the changing electorate could affect political fortunes.

In Florida, population changes continue to shift in Obama’s favor, largely because the Cuban American share of the Hispanic population, which votes Republican, continues to fall as the non-Cuban Hispanic share rises. Today, non-Cuban Hispanics represent a majority of the Latino vote in the state, and depending on which part of Latin America they come from, Obama can expect to win anywhere from 60 to 75 percent of their votes. Older Cuban Americans are being supplanted by younger non-Cuban Hispanic voters.

In Nevada, the big shift has been the increase in Latino voters. That helped Obama win a comfortable victory there in 2008. However, the state’s economic woes virtually guarantee a close race there this year. Nevada has among the highest unemployment rates in the nation, and the housing collapse brought major foreclosures and left a majority of homeowners underwater on their mortgages. Obama will need heavy turnout and a strong vote from the Latino community to win the state.

Republicans already have put North Carolina into Romney’s column. Obama carried the state by just three-tenths of a percentage point in 2008, and Republicans see virtually no way for him to replicate that success in November. Still, the Obama team still holds out hope of winning — because of the particular makeup of the electorate.

Obama advisers expect him to win an overwhelming share of the African American vote again. But they also see enough white voters as potential Obama supporters to carry him to victory. That’s because North Carolina continues to attract white voters from other parts of the country, and those new residents, many of them well educated, are more likely to support Obama than are those born in the state.

In an election as close as this presidential race may turn out to be, many things could tip the balance: a notable change in the unemployment rate, an overseas crisis, a major gaffe in one of the debates, even, perhaps, spending by the super PACs. But at the margins, demographics will make a difference, too.

For previous columns by Dan Balz, go to