The U.S. presidential race is a tossup as Democratic presidential candidate Barack Obama has lost what was once an eight-point lead over Republican rival John McCain, according to a new poll.

The Washington-based Pew Research Center for the People and the Press said Wednesday that Obama now leads McCain 46 percent to 43 percent among registered voters, down from June when the Illinois senator enjoyed a 48 to 40 advantage. His lead narrowed to five points in July, the survey said.

The nonpartisan group attributed the shift to McCain's progress winning over core Republican voters, including white evangelical Protestants along with white working class voters. By contrast, the poll said, Obama has made "little progress" expanding his support among Democrats over the past two months.

Obama has made "no significant headway" among Hillary Clinton's former supporters, with 72 percent of them saying they now back Obama. That's unchanged from last month and 3 percentage points higher than in June, Pew said.

Still, the report said Obama's supporters tend to be more enthusiastic about his candidacy, with 58 percent saying they "strongly" back him. Thirty-nine percent of McCain's supporters said they felt similarly about his campaign, the survey said.

The poll said voters see McCain as more likely to "use good judgment in a crisis" and more willing to take "unpopular stands." Obama got better marks when respondents were asked which candidate has "new ideas," "connects well with people" and "shares my values," the poll said.

Divided Electorate

The poll said the electorate remains divided by race, age and sex. Eighty-eight percent of blacks said they favor Obama while McCain enjoys a dozen-point lead among whites. Men prefer McCain by eight points and women favor Obama by 13 points, the survey said. It found Obama with a 24-point lead among those younger than 30 while McCain has a five-point lead among voters older than 50.

The candidates are in a dead heat among independent voters — one-third of the electorate — with 12 percent favoring Obama, 11 percent backing McCain and 10 percent undecided, according to the poll.

The survey of 2,414 registered voters was conducted from July 31 to Aug. 10 and has a margin of error of plus or minus 2.5 percentage points.