On the eve of critical primaries in North Carolina and Indiana, yet another pollster shows a significant shift in support among Democrats nationwide to Hillary Clinton. AP/Ipsos had Barack Obama leading Hillary by three points one week earlier, but their latest survey now has Hillary ahead by seven:

The latest Ipsos poll conducted over the weekend shows that on the eve of the Indiana and North Carolina primaries, Democratic candidate Hillary Clinton has taken over the lead in popular support from Democrats nationally. Among Democratic supporters across the country, 47% say that if the 2008 Democratic presidential primary or caucus was being held in their state today, they would choose Clinton, while 40% would vote for Barack Obama.

These results are in contrast to a poll conducted by Ipsos from April 23rd to April 27th and released last week which showed that Obama had a forty-six percent to forty-three percent lead over Clinton on this same question. Democratic support for Clinton remains highest from women (51%), who have a high-school education or less (58%), and very low income respondents (57% among those with an annual household income of $25,000 or less).

The poll also shows both Democrats leading McCain by four (Obama) or five (Hillary), but like the NYT/CBS poll, the sample looks rather suspect. Ipsos polled 1,000 adults, 755 of whom were registered voters. Democrats or Dem-leaners constituted more than half of the overall sample at 514, while only 317 were Republicans or GOP leaners. Under those circumstances, the closeness of McCain — who has generated little media coverage in the last few weeks — indicates that the Democrats may have some serious problems in the fall.

For the purpose of trending among Democrats, though, the poll suffices nicely. A ten-point shift in a week with the same pollster demonstrates a significant reversal for Barack Obama, at least for the moment. The effects of Jeremiah Wright and perhaps William Ayers appear to have created momentum away from Obama, and Democrats may well wonder whether Obama can beat anyone at this point in time, let alone John McCain in November.

The question for Hillary will be whether this surge came too late. She needed this kind of movement in the polls in February, before the Obama nomination really got sold as a fait accompli. Hillary has enough evidence of Obama’s faltering campaign, but the superdelegates may be too afraid of the backlash if they act on it now. Voting for Hillary now looks like stealing the nomination from Obama, and it will take a lot of convincing before they can do that and sell it as the best decision for the party.

That makes North Carolina a critical contest. If Obama can’t beat Hillary convincingly there, she can point to a loss of confidence across the Democratic spectrum. If she actually wins — a long shot, but not impossible — Obama may have to start making a better argument for the nomination than his February momentum.