Less than six weeks away from America’s election day, President Obama is—to an unexpected degree—reassembling the potent coalition of support that powered his breakthrough victory four years ago. And that could solidify voter allegiances in a way that creates opportunities for Democrats, and challenges for Republicans, far beyond this November.

In 2008, Obama assembled what I called at the time a “coalition of the ascendant,” meaning that he performed best among groups that are growing in society. This coalition rested on three central pillars: young people, minorities, and college-educated whites, especially women.

In his historic victory, Obama carried a combined 80% of the vote among minorities (including not only 95% of African-Americans but two-thirds of Hispanics); two-thirds among voters younger than 29, most of them part of the massive “Millennial Generation” (born between 1982 and 2002); and just under half of college-educated whites (including a 52% majority of college-educated white women.) That was enough to allow Obama to comfortably withstand a strong tilt toward John McCain, the Republican candidate among blue-collar and older whites—the same groups that had anchored the Democratic coalition in the first decades after World War II. In fact, Obama became the first American candidate to lose whites overall by double-digits and still win the presidency.

Obama’s strength with these emerging blocks presented a great opportunity to Democrats, because all of them are steadily growing as a share of the electorate—mostly at the expense of the blue-collar whites so critical to Republicans. The minority share of the vote has swelled from 12% when Bill Clinton was first elected in 1992 to 26% in 2008 and could hit 28% this year. The number of Millennials eligible to vote will soar from around 40 million in 2008 to nearly 60 million in 2012, according to Morley Winograd and Mike Hais, co-authors of two books on the generation. White college graduates have remained steady at about one-third of the electorate since the early 1990s, but the internal balance among them is shifting toward women, who consistently vote more Democratic than their male counterparts. (Women now earn almost three-fifths of all college degrees among whites, federal figures show.)

Meanwhile, blue-collar whites, now the cornerstone of the Republican coalition, have declined from a 53% majority of all voters in 1992 to just 39% in 2008 and will likely contract a bit more in 2012.

Obama’s hold on his emerging coalition loosened amid the continuing economic strain and intense partisan polarization of his first two years. Compared to Obama’s showing in 2008, exit polls found that Democratic House candidates in 2010 lost ground with minorities, young people and college-educated white women. Among minorities and young people, turnout plummeted as well.

None of this was shocking. Unemployment among Hispanics, African-Americans and young workers has remained in double-digits every month of Obama’s presidency. Those trends had many Democrats expecting that turnout and Obama’s margins would again shrink this year among the major groups in his new coalition.

But over the past year, Obama has systematically launched initiatives that target this coalition—even at the price of further alienating culturally-conservative older and blue collar whites. Obama has embraced gay marriage; insisted employers provide free access to contraception in health insurance (despite howls of protest from the Catholic Church); picked a fight with Congressional Republicans to maintain subsidized student loan rates; and acted administratively to temporarily legalize “the Dreamers,” young illegal immigrants brought to the country as children by their parents. Romney cooperated by moving sharply right during the Republican primaries on both immigration and social issues (like contraception and funding for Planned Parenthood, which provides birth control and abortions), thereby alienating key elements of Obama’s coalition.

The result is that Obama moves into the campaign’s final month with brighter prospects than almost anyone expected to reassemble, and perhaps enlarge, his 2008 coalition. An Allstate/National Journal Heartland Monitor Poll released on Sept. 27 showed the president drawing 63% of voters under 29; 78% of all non-white voters; and 50% of college-educated white women—enough to power him to an overall lead over Romney of 50% to 43%. In the key battleground states, like Ohio, Florida and Virginia, recent polls show Obama running at least that well with these groups, particularly with minorities and the upscale white women. And, while turnout for minorities and young people remains a Democratic concern, polls show more of them expressing interest in the contest.

This race suddenly presents the risk to Republicans of becoming what Winograd calls “a confirming election” that solidifies the Democratic allegiance of this coalition of the ascendant, particularly the Millennials. “Once you have a generation that votes the same way two elections in a row [it’s tougher to reverse],” Winograd says. “That’s what I think you are seeing in these latest poll numbers.”

In today’s media-saturated world it’s not clear that either party can establish the sort of lasting hold on voters triggered by earlier realigning presidential elections, like Abraham Lincoln’s victory in 1860 or Franklin Roosevelt’s in 1932. But an Obama victory that largely reassembles the coalition that elected him in 2008, despite the greatest economic upheaval since the Depression, would send Republicans a stark warning. “If Romney loses, everyone will be complaining about [chief strategist] Stuart Stevens or candidate attributes, but the number one reason will be the shrinking size of the demographics we have a competitive position in and the rising size of the demographics in which we don’t,” says veteran Republican strategist Mike Murphy, a former Romney adviser. “We have to face that reality….Denial has to end.”