By David Paul Kuhn - June 22, 2012

President Obama does not currently have enough white support to win re-election even if he retains his minority base from 2008. At the same time, electoral data indicates Mitt Romney has not yet attracted enough of these white voters to capitalize on Obama's weakness.

Pundits often note that Romney cannot win with his current level of Hispanic support. That's likely true. But so is the converse: Obama cannot win with his level of white support unless white swing voters withhold their votes from Romney as well.

Today, fewer whites back Obama than any Democratic candidate since Walter Mondale. Romney does not need to emulate Ronald Reagan to win. Should he match Reagan’s share of the white vote in 1984 -- presuming all else remains constant since 2008 -- Romney would rout Obama.

Of course, America has changed since Reagan. Non-Hispanic whites were 89 percent of the electorate when Reagan first won the White House in 1980. They were 85 percent in 1988. By 2008, whites were 74 percent. That shift has upended the electoral landscape. But only so much.

Take Michael Dukakis’ fate as an example. In 1988, George H.W. Bush’s margin of victory exceeded Obama’s in 2008. But if Obama’s level of white support in 2012 equals Dukakis’, and all else remains the same from 2008, Obama would likely narrowly win. He would lack a mandate and risk immediate lame-duck status. But he would survive with white support that once sundered Democrats.

Unless . . .

What if Obama doesn't even match Dukakis with whites? That’s the dynamic of 2012. This electorate has a white floor. And it has broken for this president. Democrats cannot depend on demographics to save them.

Should Romney win the whites Obama lost, Romney will only need to perform as well as John McCain with minorities to win. This is true even under Democrats’ most optimistic, and unlikely, demographic scenario: that the white share of the electorate decreases another two percentage points from 2008, blacks turn out at the same historic levels they did then, and the Hispanic share of the vote rises from 9 to 11 percent of the electorate while Obama retains the same level of support from other minority groups.

The white margin to watch: 61-39. That’s the rough break-even point. Obama likely needs more than 39 percent of whites to assure re-election. Romney likely needs at least 61 percent of whites to assure Obama’s defeat (or 60.5 in some scenarios). These are estimates based on an electorate that matches the diversity of 2008 or is slightly less white. It presumes the Electoral College outcome does not diverge from the winner of the popular vote (loose talk aside, it’s only happened four times in U.S. history).

Thus, Obama can do a little worse than Dukakis, and Romney must perform a little better than Bush circa 1988. Whites favored Reagan in 1984 by a 64-35 margin. They favored Bush in 1988 by a 59-40 margin. Four years ago, whites favored McCain by a 55-43 margin.

Only 37 or 38 percent of whites back Obama today, according to the Gallup Poll’s authoritative weekly averages since early April (which have a larger sample size than most polls combined). The rub for Romney? In those same matchups, Romney only wins 54 percent of whites. Other surveys show the same. CNN’s latest pegged the white margin at 53-39. FOX News’ latest, 51-35. Ipsos-Reuters, 53-38. The Pew Research Center's polls have, however, shown Obama stronger this year. Its recent survey placed the margin at 54-41.

Writ large, Obama appears below his floor with whites. But so does Romney. Obama has too few whites saying yea to a second term. And Romney has converted too few nays to his side. Notably, the same share of whites say they will vote for Obama as approve of his job performance.

These whites constitute, by far, the largest share of the swing vote. The president depends on Hispanics to partly compensate for his weakness with whites. That’s possible in some states like Florida, Colorado and Nevada. But Latinos are less than a 10th of the electorate in every other swing state.