As has been widely noted, Obama’s weakest voter group by far is the white working class. That is true today as it was true in the 2008 election, when Obama lost white working class voters by 18 points, but white college graduates by only 4 points. (The closer you look at the numbers from 2008, the starker Obama’s problem with this demographic reveals itself to be: It is true, for example, that the white union vote overall was slightly Democratic (52-47), but that figure conceals that fact that Obama actually lost the unionized white working class (46-52) while carrying unionized white college graduates by a solid 58-41.)

Huge deficits among these same voters routed the Democrats in 2010. And Obama appears to be weaker among this group today than he was back in 2008. Yet Obama is running ahead consistently in the national and swing state polls. Why is the Obama coalition not yet succumbing to its clear Achilles’ heel?

There are two reasons. The first is that the rest of Obama’s coalition has held up so well. The minority vote looks rock solid for Obama, coming very close to the 80 percent support level he received in 2008. This is due to overwhelming backing from black voters plus support among Hispanic voters that meets or exceeds 2008 levels. In addition, judging from eligible voter trends, minorities should be a larger share of voters in 2012 than 2008. Also, Obama may have actually gained ground among college-educated whites. In Pew polls, this group is averaging around a 2 point deficit for Obama, compared to 4 points in 2008.

This gives Obama a considerable buffer against expected weakness among white noncollege voters. Indeed, if the minority and white college-educated vote hold up as well in November as they have in recent polling, Romney needs to generate a huge margin among white working class voters to have a decent chance of winning—closer to the 30 points Congressional Republicans won this group by in 2010 than the 18 point margin received by John McCain in 2008.

That brings us to the other reason Obama has been ahead so consistently in the polls. Romney has not been remotely close to that level of support among white working class voters. He’s been averaging around the same margin McCain received in ‘08 with occasional readings as high as 23 points. Even the latter margin is far off what he will need to win, given the size and leanings of the rest of the electorate.