Obama led Romney 51 percent to 41 percent in the survey of 1,956 registered voters, which has a margin of error of plus or minus 3.2 percentage points. It was conducted July 16-26.
Obama's advantage is narrower in 12 swing states that will be key to the November election, the survey by the Washington,D.C.,-based center showed. When only Colorado, Florida, Iowa, Michigan, Missouri, New Hampshire, North Carolina, Ohio, Pennsylvania, Virginia, Nevada and Wisconsin are considered, Obama's lead is 48 percent to 44 percent.
Romney's unfavorable rating rose to 52 percent, from 47 percent in Pew's previous survey, while Obama's unfavorable rating dipped to 45 percent, from 48 percent.
The survey of 2,508 adults, including 1,956 registered voters, was conducted before Romney completed a trip to Britain, Israel and Poland, which was marked by a series of gaffes.
In the sample, 33 percent of respondents identified themselves as Democrats and 22 percent as Republicans. Among the registered voters in the poll, 38 percent identified as Democrats while 25 percent as Republicans, according to Pew.
Obama's campaign ran 35,347 television ads during the 14- day period ending July 16, according to New York-based Kantar Media's CMAG. By comparison, the Romney campaign aired 16,946 spots during that period. More than 97 percent of those ads were negative, meaning voters saw twice as many campaign-funded commercials attacking Romney rather than Obama.
Later this month, former President Bill Clinton will appear at an event in New York hosted by Priorities USA Action, a super-political action committee supporting Obama's re-election bid, according to a person familiar with the plans who spoke on condition of anonymity. Clinton is also scheduled to speak at the Democratic National Convention next month.
The organization, founded by former White House aides Bill Burton and Sean Sweeney to counter Republican fundraising groups, reported raising $6.2 million last month. Priorities expects to raise and spend $100 million by the Nov. 6 election, Burton said last month on Bloomberg Television.
Super-PACs can take in unlimited corporate, union and individual donations. The super-PACs are barred from making donations to candidates, and can spend money independently of the campaigns.
-- With assistance from Jonathan D. Salant, Hans Nichols and Greg Giroux in Washington.
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