But the most interesting finding is among whites with incomes of under $50,000: His negative numbers among them have jumped 20 points, from 29 percent to 49 percent.

Today's ABC/poll makes clear how unpopular both Mitt Romney and Newt Gingrich are and how much more unpopular they have become recently as they battle for the Republican presidential nomination. That's a broad point to be taken from the poll, but Greg Sargent also points to a specific result that could spell trouble for Mitt Romney:

It's hard to overestimate the importance of this group in elections:

Sargent continues:

If Romney proves unpopular among these voters, it’s not impossible that Dems could win them back in the numbers they need next year. It’s true that Obama’s numbers among them remain worse than Romney’s; his negative rating is 56 percent. But according to a recent Center for American Progress study, Obama only has to limit his losses among this demographic in order to win reelection, provided he does reasonably well with upscale, college-educated whites — and today’s Post poll finds he’s rising with that group.

Let's be clear that "limiting his losses" with this group does not mean Obama can sit back. But with Romney's tax returns illustrating just how far-removed his life is from working- or middle-class concerns, a Romney nomination would definitely open the door to make the clear and accurate case that Obama's policies are better for working people.