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Barack Obama's job approval rating flattened at an even 47-47 percent in the latest ABC News/Washington Post poll, his lowest in more than a year, with more than half of Americans disapproving of his handling of the situation with Syria.

The public by a 15-point margin is more apt to say Obama's performance on Syria has weakened rather than strengthened U.S. global leadership, and six in 10 continue to oppose the missile strikes he urged. At the same time, the survey finds vast support, 79 percent, for the Russian-backed plan to junk Syria's chemical weapons, even amid skepticism Syria will cooperate.

See PDF with full results, charts and tables here.

If Syria in fact fails to surrender its chemical weapons, the public divides about evenly on whether Congress should authorize military strikes after all: Forty-four percent say it should, short of a majority but well more than the 30 percent who back missile strikes as things stand now.

There are some positive notes for the president. More than half, 54 percent still see him as a strong leader; 52 percent say he's a good commander-in-chief of the military; and more, 60 percent, say he sticks with his principles. On Syria specifically, more accept than reject his argument that the threat of missile strikes helped the situation, albeit by a single-digit margin, 47-40 percent. Similarly, he leads congressional Republicans in trust to handle the confrontation with Syria by 8 percentage points.

More Americans in this poll, conducted for ABC by Langer Research Associates, found Obama's address to the nation on Syria last week to be persuasive rather than unpersuasive, by 47-32 percent. However 21 percent have no opinion on the speech, and as often occurs in such cases, some critics may just have tuned him out.

VITAL INTEREST? - Most import on Syria is the question of whether or not the situation involves the vital interests of the United States, as Obama has argued. Support for strong action rises in cases when U.S. interests are seen as being at stake; for instance, 67 percent said so about Iraq in 2003, vs. just 23 percent about Somalia in 1993.

On Syria, it's a split decision: Forty-five percent of Americans see vital U.S. interests at stake in this situation, while 48 percent do not. Liberals are most likely to see the issue as one of vital concern, with 55 percent saying so; fewer moderates and conservatives agree, 43 and 42 percent, respectively.

It matters: People who see vital U.S. interests at stake are 16 points more apt than others to favor missile strikes now (though most still don't) and 23 points more apt to favor having Congress authorize military action if Syria fails to cooperate. Should Syria stall, support for congressional authorization reaches 56 percent among people who think vital U.S. interests are involved, vs. 33 percent among those who think not.

SUMMARY NUMBERS - In summary, some of the topline results of this survey, in context, are as follows:

• At 47-47 percent, Obama's overall job approval rating is its lowest since July 2012. More "strongly" disapprove than strongly approve by 12 points, the largest negative gap in intensity of sentiment about his performance since farther back, January 2012.

• Americans give Obama a 47-44 percent approval rating for handling international affairs overall, with approval down 7 points from a post-re-election bump. His approval turns negative, 36-53 percent, on Syria specifically, with views on his handling of the situation there more strongly negative than strongly positive by a broad 20 points, 19 vs. 39 percent.

• Sixty-one percent oppose missile strikes on Syria, vs. 30 percent in support, similar to ABC/Post polls the past two weeks. By contrast, the public supports the Russian plan by 79-16 percent, even though 68 percent lack confidence Syria will cooperate with the collection and destruction of its chemical weapons by international monitors.

• As noted, substantially more think Obama's handling of the situation with Syria has weakened rather than strengthened U.S. leadership in the world, 32 vs. 17 percent. But a plurality, 46 percent, don't think it's affected perceptions of U.S. leadership either way.

• Views of Obama as a strong leader, while down by 7 points from early this year, are more positive than negative for the 10 th time in 11 ABC/Post polls to ask this question. His rating as a commander-in-chief is better than his prospective ratings on this question before he took office. While sticking with his principles is a notable strength, he gets an even split on another personal attribute, whether or not he "shares your values." That's been the case steadily since late 2010, with very wide partisan and ideological divisions.

GROUPS/OBAMA - Even beyond the customary political gaps, demographic groups divide sharply in their assessments of Obama. His job approval rating is 74 percent among nonwhites vs. 33 percent among whites (with a sizable gap between college-educated vs. non-college whites - 40 percent approval in the former group, 28 percent in the latter).

Obama's approval rating reaches 57 percent in urban areas, 55 percent in the Northeast and 55 percent among 18 to 29-year-olds. He holds 54 percent approval in the blue states he won in 2012, vs. 35 percent in the red states.

While now usual, the political divisions are huge. Eighty percent of Democrats approve of the president's performance overall; 10 percent of Republicans agree. (It's 42 percent among independents.) Sixty-seven percent of liberals approve vs. 26 percent of conservatives. (It's 52 percent among moderates.) For his worst rating, look to conservative Republicans, a group in which just 6 percent approve of Obama's work in office, while 92 percent disapprove. Eighty-three percent disapprove strongly.

Obama loses ground in his own base and in the center alike when it comes to handling the situation with Syria. Sixty percent of Democrats and 55 percent of liberals approve, as do just 32 and 37 percent of independents and moderates - lower in each case than his approval overall in these groups.

Independents divide on whom they trust more to handle the situation with Syria, Obama or the Republicans in Congress, 36 to 34 percent; in a notable expression of their political disaffection, 21 percent of independents volunteer that they don't trust either option. Obama and the GOP each win three-quarters of their partisans on this question, with Obama prevailing because self-identified Democrats outnumber Republicans by 11 points.

GROUPS/SYRIA FORCE - Given widespread public expectations that Syria won't in fact cooperate with the Russian plan to neutralize its chemical weapons stockpile, it's instructive to know which groups support or oppose an authorization of force by Congress as a backup plan.

Beyond the "vital interests" result, politics and ideology again play a substantial role. Support for authorization of force if Syria doesn't comply reaches majorities among just a few groups in this survey - Democrats (56 percent) and liberals (53 percent), and among two strongly Democratic groups, blacks and nonwhites overall (63 and 58 percent).

Even those numbers are comparatively tepid, given that they're core Obama support groups. Were the Russian plan to fail and Obama to return to Congress for authorization, these results suggest he'd face a further difficult battle for public opinion - unless and until the case is made that vital U.S. interests are in fact at stake.

METHODOLOGY - This ABC News/Washington Post poll was conducted by telephone Sept. 12-15, 2013, in English and Spanish, among a random national sample of 1,004 adults, including landline and cell-phone-only respondents. Results have a margin of sampling error of 4 points, including design effect. Partisan divisions are 34-23-34 percent, Democrats-Republicans-independents.

The survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by Abt-SRBI of New York, N.Y.