AP Photo

Rick Santorum's popularity has jumped since his Feb. 7 trifecta, matching Mitt Romney's among Republicans, surpassing Romney among very conservative Americans and putting Santorum ahead in strength of sentiment, potentially an important factor in the GOP contest.

Romney also has gained some ground among strong conservatives, and both candidates are popular with six in 10 Republicans. But the latest ABC News/Washington Post poll finds both well below the levels of favorability enjoyed by front-runners in either party four years ago.

Santorum's popularity has levitated to 61 percent and 67 percent, respectively, among Republicans and very conservatives, up from 48 percent in both groups last month. That follows Santorum's wins in the Colorado and Minnesota caucuses and Missouri's beauty contest primary last week.

Notably, Santorum leads Romney in "strong" favorability among key groups in this poll, produced for ABC by Langer Research Associates. Romney is seen strongly favorably by just 13 percent to 19 percent of Republicans, conservatives, very conservatives and conservative Republicans. Santorum reaches 33 percent strong popularity in the latter two groups, boosting him to a 26 percent strongly favorable rating among all Republicans, 9 points ahead of Romney.

Still Romney, while trailing Santorum among very conservatives, has clawed back some ground in this group, one in which he's struggled to win consistent support. Fifty-four percent of very conservatives now see Romney favorably, vs. 43 percent late last month, his low this cycle.

Romney, who won the lightly attended Maine caucuses last weekend, has a 60 percent favorability rating among Republicans overall, essentially the same as Santorum's, and 63 percent among conservative Republicans, compared to Santorum's 69 percent.

These ratings indicate that both candidates are basically acceptable to majorities within their party. But at 60 percent and 61 percent among Republicans, Romney and Santorum's ratings are well behind those of John McCain, who had 76 percent, and Rudy Giuliani, 71 percent, among Republicans in an ABC/Post poll in January 2008. Romney was at 58 percent in that poll, very similar to where he is now; Mike Huckabee was at 65 percent. In that same survey, Hillary Clinton had an 85 percent favorability rating among Democrats, Barack Obama 80 percent, John Edwards 72 percent - again all substantially higher than Romney and Santorum in their party today.

Beyond the GOP, Romney has improved among independents, the traditional swing voters in national elections. While a tepid 37 percent of independents see him favorably, that's up from just 23 percent late last month. Santorum's rating among independents is similar, 35 percent favorable, up by 9 points since an ABC/Post poll last measured his popularity in early January.

For comparison, Huckabee and Giuliani were in the low 40s in favorability among independents in early 2008, while McCain, Obama and Clinton all were viewed favorably by at least six in 10 independents, well over Romney and Santorum's levels now.

OVERALL - Both Romney and Santorum have improved from last month in terms of their general popularity, but also face obstacles. Romney, whose favorability rating among all Americans went under water late last month, remains there, albeit by less of a margin. Thirty-six percent of Americans now see him favorably, 43 percent unfavorably; it was 31-49 percent in late January.

Santorum's in a bit better shape, but perhaps because more have yet to form an opinion of him. Thirty-six percent of Americans see him favorably, identical to Romney's rating; fewer, 31 percent, see Santorum unfavorably. A substantial 33 percent have no opinion of Santorum one way or the other; that's eased from 44 percent last month, with the shift almost all in his favor.

Romney's favorability rating among all Americans now is similar to his 34 percent in January 2008. As is the case among Republicans and independents, other candidates in 2008 were more popular with the public overall than are Romney or Santorum today: Obama, 63 percent; McCain, 59 percent; Clinton, 58 percent; Edwards, 57 percent; Giuliani, 46 percent; and Huckabee, 42 percent.

Among other groups, reflecting patterns of partisanship, Santorum and Romney both are more popular among higher-income, middle-aged and older Americans and whites, compared with their counterparts.

METHODOLOGY - This ABC News/Washington Post poll was conducted by landline and cell phone Feb. 8-12, 2012, among a random national sample of 1,009 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.