It was no fluke four years ago that America elected its first black president, and the trends that helped Barack Obama make history are evident today in demographics that favor his reelection. Millennials, the most liberal generation, are increasing at the rate of 4 million a year; there were 48 million in ’08, there are 64 million today, and Obama won them by 66 percent. Minorities too are growing as a share of the electorate, and Obama won them last time by 80 percent.

After the disappointments of the last four years, it’s unlikely that Obama will match his ’08 margins with these demographics. But to win, he has to do well enough among millennials and minorities to compensate for his weakness among white, working-class voters, who were once the core of the Democratic base and now are the GOP’s bread and butter. “A real wild card is how many of them are going to show up,” said Ruy Teixeira, a joint fellow with the Center for American Progress. “He can win with 75 percent; if he gets 80, that doesn’t make him bulletproof,” but it does make him “a slight favorite, but he certainly could lose.”

More single people, secular people, and people with college degrees are all part of what Teixeira calls a “warming trend” toward Democrats. White, working-class voters, the group most resistant to Obama, were 28 percent of the electorate in ’08, and they’re down another 3 percent this year. But that’s a national number; in Ohio, a battleground state, they are 54 percent of the electorate. No Republican has won the White House without Ohio, so it’s not surprising that Republican Sen. Rob Portman, who has won statewide in Ohio, tops the list of prospective running mates for Mitt Romney.

The white working class is “plummeting” as a share of voters, said Teixeira, replaced by white college graduates and minorities. Democratic nominee Michael Dukakis lost white, working-class voters by 20 points and with them the 1988 election; Obama lost them by 18 points in 2008 but still won. “Even if Obama lost working-class whites by 23 points, he could still win the election because the country has changed so much,” said Teixeira. The demographic shifts mean Dukakis and John Kerry would win too if they were running in today’s electorate.

The flip side of this argument is that Romney needs to do really well among working-class whites, carrying them by as much as 25 points over Obama to compensate for the GOP’s weakness among minorities. In ’08, John McCain carried working-class whites in Ohio by just 10 percent, and he lost the state. Romney has just a 6 percent lead among this group, “and that is fatal,” said Teixeira.

Confronted with this all this data favoring Democrats at a discussion sponsored by the Bipartisan Policy Center, Sean Trende, a senior elections analyst at Real Clear Politics, cautioned against expecting current trends to last far into the future. If he were making predictions in 1924, he said, he would have said African-Americans, loyal Republicans since the Civil War, would remain so, and that the South would continue as the bedrock of the Democratic Party. Ten years out, those predictions looked shaky; decades later they were laughable.

The alternative scenario offered by Trende assumes the immigration wave now benefiting Democrats stops; and that Latinos’ voting behavior shifts as they remain in this country, make more money, and their children and grandchildren go to professional schools. “The long-term trend is slightly toward Republicans,” Trende said. He noted that last year, there was net migration back to Mexico, a trend recently confirmed by a Pew Research Center survey that found immigration from Mexico “has come to a standstill.”

The history of political parties is that over the long term they adjust to changing demographics and evolving attitudes. Trende predicts that by the time his young children are in college, the GOP will embrace gay marriage. And Teixeira said the Democratic Party, if it wants to retain the loyalty of Hispanics and young people, will have to deliver for them on economic growth and opportunity. “They can’t just rely on protecting Medicare and Social Security,” he said.

In the short term, though, there is a less harmonious scenario, a “racialized” politics that will play out over the coming months as the GOP doubles down on the share of the electorate it must carry by a big margin, those white working-class voters. Teixeira points to Pennsylvania, a state Obama carried by 10 points in ’08, and where there are ongoing and sharp decreases in the white working class, which means Romney has to drive up his share of that diminishing group. “You’ve got to heavily racialize the white vote in Pennsylvania to squeeze everything you can get,” said Teixeira.

Evidence of this racialization is evident in Arizona, said Trende, where Gov. Jan Brewer “did everything she possibly could to alienate Latinos.” Running for reelection in 2010, Brewer ran behind McCain with Hispanics, but ahead of him by 6 or 7 points among whites as he won reelection to the U.S. Senate. Arizona’s crackdown on illegal immigration is now before the Supreme Court, where a ruling is expected in June and likely to intensify the ongoing demographic divide, whatever the justices decide.