Mitt Romney has fallen to a new low in personal favorability among strong conservatives in the latest ABC News/Washington Post poll, as his persistent problems in this core GOP group now threaten his fortunes in today's crucial Michigan primary.

Nationally just 38 percent of Americans who identify themselves as "very" conservative hold a favorable opinion of Romney, down 14 points from last week to the fewest in ABC/Post polls in this election cycle. Far more in this group, 60 percent, express a positive view of Rick Santorum.

Romney is at new lows among related groups as well, with 56 percent favorability among conservative Republicans and 40 percent among all conservatives, down from last week by 13 and 10 points, respectively. But the comparison with Santorum is most striking among very conservatives, the highly ideological and predominantly Republican group on which Santorum has based his campaign strategy.

This poll, produced for ABC by Langer Research Associates, finds that Romney comes back in less ideologically committed groups; 58 percent of Republicans have a favorable opinion of him overall. While that's a tepid rating in his own political party, he has company: Santorum's in almost exactly the same position among all Republicans, with 59 percent favorability.

Among customarily swing-voting independents, just 32 percent see Santorum favorably, 29 percent Romney, similar ratings that indicate the challenges either may face in the general election. Romney's underwater among independents - 44 percent see him unfavorably. Santorum manages a split decision, with more undecided.

OBAMA - Almost no one's undecided on Barack Obama: He also comes in at a split decision among independents, with a 49-48 percent favorable-unfavorable rating. But Obama soars among Democrats - 83 percent see him favorably - in a way that neither Romney nor Santorum does in their own party, which clearly has yet to coalesce around its choice for November.

Obama's popularity plummets among Republicans, to 22 percent, about the same as Santorum and Romney get from Democrats. The president lands at a 51-45 percent favorable-unfavorable rating overall - far from a ringing endorsement, but unlike his two top competitors' ratings, at least a net positive one.

Among other groups, there's a slight difference by region that may reflect Romney's difficulties in Michigan, where he was born and raised. In the Northeast overall (he's a former Massachusetts governor), 43 percent see Romney favorably, vs. 31 percent favorability for Santorum. In the Midwest, Romney's favorability dips to 32 percent. Santorum's is 38 percent.

At the same time there's not much difference by education and income, despite Santorum's efforts to paint himself as the working-class alternative to the wealthy Romney. Their favorability ratings, for example, among college-educated and non-college-educated whites, and among those with incomes below and above $50,000 annually, are very similar.

TRENDS - The results indicate a flattening for Obama, who advanced from a career-low 47 percent favorability in September to 53 percent a month ago, essentially remaining there now.  And they confirm a stall for Santorum, whose favorability rating has been essentially unchanged in three ABC/Post polls since mid-month, after his successes in the Colorado and Minnesota caucuses and Missouri beauty contest primary Feb. 7.

Romney, for his part, has varied from a cycle-high 39 percent favorability in early January to a low of 31 percent later last month, never breaking the 40-percent barrier. His popularity ratings, and Santorum's, are well below both Obama's and John McCain's at about this point in 2008. Then again, Obama's is, too.

METHODOLOGY - This ABC News/Washington Post poll was conducted by landline and cell phone Feb. 22-26, 2012, among a random national sample of 1,011 adults. Results have a margin of sampling error of 3.5 points. The survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by SSRS/Social Science Research Solutions of Media, Pa.