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Mitt Romney reached his highest personal popularity of the election campaign among registered voters in the latest ABC News/Washington Post poll - but not by enough to lift his head above water, nor to surpass Barack Obama, who reached his own best favorability rating of the season.

Night-to-night data indicate a sizable boost for Romney, and drop for Obama, on Thursday night, a day after their first debate, which Romney widely is seen as having won. But both of those trends subsequently subsided in this poll, conducted Thursday through Sunday.

See PDF with full results, charts and tables here.

The net effect is slight at best. Romney is now seen favorably by 47 percent of registered voters overall, unfavorably by 51 percent; Obama's rating is better, 55-44 percent. Changes for both candidates from their pre-debate levels (Romney 44-49 percent, Obama 52-45 percent) are not statistically significant, given the surveys' margin of sampling error.

Romney's 47 percent favorability is numerically the most in 18 ABC/Post polls since September 2011. But he remains underwater for the 13th time in those 18 surveys. (He's been above water three times, not since January, and even twice.)

Four previous candidates have been underwater in popularity at roughly this point in available data back to 1980: losing Democratic candidates John Kerry in late September 2004, Walter Mondale in October 1984 and Jimmy Carter in September 1980; and Republican George H.W. Bush in October 1992. In another gauge, though, just one incumbent postwar president has been re-elected with a job performance rating as low as Obama's at roughly this time, George W. Bush in 2004. (The same may have been true for Harry S. Truman; data are insufficient.)

Obama's 55 percent favorability is numerically its highest since spring 2010. Better employment numbers on Friday may have provided some respite from his debate performance; among other groups, he's at his best since March among middle- and upper-middle income earners.

More fundamentally, the results of this poll, produced for ABC by Langer Research Associates, suggest a rallying in some of each candidate's usual affinity groups. Romney's favorability ratings are his best to date among conservatives. Obama, in turn, is at his best of the election season among moderates, and his best since taking office among Democrats.

Among other groups, Obama's reached highs in favorability for this election season among whites, married men and college-educated registered voters, and matched his previous best since taking office among men overall and seniors. Romney's at a new high among women, unmarried men and adults older than 50 who are registered to vote.

Part of Obama's advantage in overall popularity stems from the fact that more registered voters identify themselves as Democrats than as Republicans; it's 36-29 percent in this survey, with 32 percent saying they're independents. Partisan divisions in the 2008 exit poll were also +7 percentage points Democratic, 39-32 percent.

METHODOLOGY - This ABC News/Washington Post poll was conducted by landline and cell phone Oct. 4-7, 2012, among a random national sample of 845 registered voters. Results have a margin of sampling error of 4 points, including design effect. 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.