The six percentage point spread is unchanged since June, when48 percent to 42 percent. But more than 1 in 10 voters now say they are undecided between the candidates - twice as many, percentage-wise, as last month - and 28 percent of those who did express a preference say they might still change their mind.
The race between McCain and Obama appears to be more fluid than the 2004 battle between Democratic nominee John Kerry and President George W. Bush. Four years ago this month, just 6 percent of those surveyed were undecided between the candidates. And only 20 percent of those asked indicated their minds weren't yet made up.
Obama voters are far more enthusiastic about their candidate: Half of his supporters described themselves as "enthusiastic" about Obama as nominee, while just 16 percent of McCain voters said the same. Sixty-eight percent of McCain voters describe themselves as "satisfied" with the presumptive GOP nominee, while 14 percent say they are "dissatisfied."
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The 2008 Campaign
Iraq and the Economy
Only six percent of Obama voters say they are "dissatisfied" with the Democratic candidate. But there are some lingering reservations among former supporters of Obama's toughest rival for the Democratic nomination, Hillary Clinton. About one in five of those who say they voted for Clinton in the primaries now plan to support McCain in November. And just 29 percent of former Clinton supporters who plan to vote for Obama feel "enthusiastic" about the candidate.
Just less than half of those surveyed want more choices in the election, a response that is similar to previous election cycles. Sixty percent of McCain supporters want more choices, while less than half as many Obama supporters say the same.
More than two in three Obama supporters say it is extremely or very important that the Illinois senator win in November. Just over half of McCain voters feel the same way about their candidate.
The War In Iraq, The Economy And Energy:
Americans are increasingly positive about the way things are going in Iraq, though a majority still believes the war is going badly.
Forty-five percent say the war is going well, up ten percentage points from last month and the most positive assessment of the situation since January 2006. But nearly sixty percent of those surveyed maintain that the U.S. should have stayed out of Iraq.
The economy and jobs are seen by nearly 40 percent of Americans as the most important problem facing the country, easily eclipsing the war in Iraq and gas prices, each of which were cited by 16 percent of respondents.
Fewer than 1 in 5 Americans describe the state of the economy as good. Eighty percent say it is in bad shape - with 35 percent describing it as "very bad." More than two thirds of Americans say the economy is getting worse, while a mere three percent say it is getting better. Still, three in four say their own household finances are at least somewhat good.
Mr. Bush's job approval rating stands at 28 percent, up slightly from last month's all-time low of 25 percent. Just 20 percent of those surveyed approve of the president's handling of the economy, the lowest percentage of his time in office.
Fourteen percent of Americans say the country is heading in the right direction, unchanged from last month's all-time low. More than 80 percent say it is on the wrong track.
McCain has proposed that the U.S. build more nuclear power plants to generate electricity, and 57 percent of Americans say they support doing so - up 12 points from April of last year and the highest percentage since 1977.
Americans are skeptical about the prospect of the next president lowering the price of gas. Only 30 percent think Obama's energy policies will help lower the price, and just 25 percent think McCain's politics will do so.
Sixty-five percent of Americans say gas prices have caused financial hardship for them or their households, and more than a third characterized their hardship as serious.
The Candidates' Support:
Following in the footsteps of every Republican presidential candidate since 1964, McCain leads the Democratic candidate among registered white voters. (The margin is nine percent.) Obama leads overwhelmingly among blacks, 89 percent to 2 percent, while Hispanics favor Obama by a wide margin, 62 percent to 23 percent.
Obama, unsurprisingly, leads among liberals and Democrats, while McCain leads among conservatives and Republicans. Independents are nearly split, with 38 percent backing Obama and 35 percent backing McCain. Nearly one in 5 independents is undecided, and 33 percent of those who have chosen a candidate say they could change their mind.
Both women and men prefer Obama, though the margin is higher among women (9 percentage points) than among men (3 percentage points). Voters under 65 support Obama, particularly those between 18 and 29 years old, where there is a 12 percentage point difference between the candidates. Voters 65 and older favor McCain by a small margin.
Working class whites favor McCain over Obama 45 percent to 33 percent, and weekly churchgoers favor the presumptive GOP nominee 52 percent to 34 percent.
Both candidates have lost credibility over the course of the campaign, though Obama's has slipped slightly more than McCain's. Just 43 percent of registered voters believe Obama says what he believes, not just what voters want to hear. That's down from 53 percent in May. Forty-six percent believe McCain says what he believes, down from 51 percent in May.
Slightly more than half of McCain voters - and 56 percent of Obama voters - say the candidates have changed their issue positions to get elected. About 4 in 10 of those who feel that way say the change has made them think worse of the candidates.
Obama's decision to opt-out of public financing in the general election - after initially vowing to work to accept it - is not a big issue for many registered voters: 45 percent say they haven't heard enough about the issue to have an opinion. One in three approve of the decision, while 18 percent disapprove.
Obama suffers from a significant patriotism gap: 73 percent of voters describe McCain as "very patriotic," while just 37 percent view Obama that way. Obama has improved on this measure, however: In April, just 29 percent considered him "very patriotic."
McCain also fares better on the question of who would be an effective commander in chief. Forty-six percent say McCain would "very likely" be effective, while just 24 percent say the same of Obama. Thirty-six percent say it is "not likely" Obama will be effective.
Forty-eight percent of registered voters believe America's image in the world will get better if Obama is elected, while just 18 percent say America's image will improve if McCain is elected.
Obama and his Democratic supporters have looked to portray McCain as representing a third term of Mr. Bush's policies, and many registered voters agree: Sixty-one percent believe McCain will continue the president's economic policies, and 78 percent believe he will continue the president's Iraq policies. More than half of McCain's supporters, however, say the Arizona senator will differ from the president on the economy.
McCain will be 72 years old on Inauguration Day, which would make him the oldest president ever elected to a first term should he win. Forty-eight percent of those surveyed say McCain's age gives him experience and wisdom to be a good president, while 36 percent say his age is an impediment to do the job effectively.
The favorable ratings of both candidates have fallen in the last month, with Obama dropping two points to 39 percent and McCain falling three points to 31 percent. McCain's unfavorable rating also fell, however, to 32 percent, just one point above Obama's.
Michelle Obama is viewed favorably by 29 percent of respondents and unfavorably by 16 percent, while Cindy McCain is viewed favorably by 18 percent and unfavorably by 8 percent. Majorities say they haven't heard enough about either woman to have an opinion.
Nearly 1 in 3 registered voters say race relations in the U.S. will improve if Obama is elected president, though 17 percent expect them to get worse if he is elected. Black voters in particular expect an improvement, with 47 percent predicting as much if Obama is elected.
But Obama's nomination has not yet done much to change African-Americans' outlook about opportunity in the U.S. Nearly two in three black voters say whites have a better opportunity than blacks to get ahead in society - up from 57 percent more than eight years ago. A majority of whites say both blacks and whites have an equal chance to get ahead.
Whites earning less than $50,000 per year and without a college education tend to see equal opportunities for both races, while wealthier whites tend to feel whites have an advantage. White Republicans have a more positive view of race relations than white Democrats, who are more likely to say U.S. society gives whites an advantage in getting ahead.
African-Americans remain pessimistic about race relations in the U.S., with 59 percent describing them as bad - up 13 percentage points from March - and just 29 percent describing them as good. Whites have a more optimistic view, with 55 percent describing race relations as good and 34 percent as bad.
Both whites and blacks believe that America is ready for a black president, and large majorities of registered voters believe that both Obama and McCain's policies would treat both races equally. Black voters largely do not anticipate any favoritism from Obama, with only 4 percent of them saying Obama would favor blacks over whites as president. Sixteen percent of white voters - including 23 percent of white voters backing McCain - expect Obama to favor blacks, however. And 39 percent of black voters think McCain's policies will favor whites.
Obama holds a nearly 40 point lead among Hispanics, a group he struggled to win over in his primary fight with Hillary Clinton. Despite losing among Hispanics in all but three states during the primaries, Obama leads McCain 62 percent to 23 percent among the group.
Mr. Bush took 44 percent of the Hispanic vote in 2004 and 35 percent of that vote in 2000. The voting block is considered key in this election, particularly in swing states like Nevada, Colorado and New Mexico.
Thirty-one percent of Hispanic voters are "enthusiastic" about Obama, while just 6 percent feel that way about McCain, who has been more moderate on immigration than many of his fellow Republicans.
Forty-four percent of Hispanics identify themselves as Democrats, while 13 percent say they are Republicans and 42 percent identify as independents.