If the election were held today and Obama and McCain were the candidates, 48 percent of those surveyed say they would support Obama while 43 percent say they would support McCain. In February, Obama led McCain 50 percent to 38 percent.
If Clinton and McCain were the candidates, the New York senator receives 46 percent support to McCain's 44 percent.
In a turnaround from last month, McCain now leads both Obama and Clinton among independent voters. Obama led McCain by 10 points among this group last month, but he now trails by 8 points. Clinton trails McCain by 11 points among independents.
Obama has the highest favorable rating of the three candidates - 44 percent - followed by Clinton at 39 percent and McCain at 38 percent. Clinton, meanwhile, has the highest unfavorable rating at 41 percent, followed by McCain at 31 percent and Obama at 28 percent.
Among Democratic primary voters, Obama is only slightly preferred over Clinton, 46 percent to 43 percent. Last month Obama led Clinton by a wider margin, 54 percent to 38 percent.
Read The Complete Poll Results
Since last month, Obama's national support among male Democratic primary voters has slipped considerably, though he still retains a 53 percent to 36 percent lead over Clinton among the group. Clinton has gained ground among female Democratic primary voters, and now leads Obama among that group 48 percent to 40 percent.
Sixty seven percent of Democratic primary voters do not think their party's nominee will be decided until the convention, and 44 percent think a protracted nomination fight will leave the eventual nominee weakened for the general election. A smaller percentage - 27 percent - say such a fight will strengthen the nominee.
Democratic primary voters are generally satisfied with their choices, however: Seventy-six would be satisfied with Obama as the party's nominee and 70 percent would be satisfied with Clinton.
If Obama wins more elected delegates but Clinton becomes the nominee because of the vote of the Democratic Party insiders known as superdelegates, 36 percent of Obama supporters say they would be angry. Fifty-six percent would be disappointed, and just 8 percent would be satisfied with the outcome.
If Clinton wins more total votes but Obama takes the nomination because of superdelegates, 22 percent of Clinton supporters would be angry and 51 percent would be disappointed.
Forty-six percent of Democratic primary voters say the superdelegates should support whichever candidate wins the most votes in primaries and caucuses. Thirty percent say they should support the candidate with the best chance to win in November, while 21 percent say the superdelegates should back whomever they like.
The divisions may have as much to do with candidate preference as principle: A majority of Obama supporters want superdelegates to side with the candidate who wins the most primaries and caucuses. More Clinton backers think superdelegates should back the candidate they think can best win in November.
Can The Candidates Deliver?
Registered voters are skeptical as to whether any of the presidential candidates can deliver on some of their stated promises if they succeed in capturing the White House.
More than half do not think Clinton will be able to deliver on her promise to provide health care to all Americans. More than half do not think Obama will unite Democrats and Republicans if he is elected president. And more than half do not think McCain will deliver on his promise to cut government waste and spending.
Voters give all three candidates similar marks on their ability to make the right decisions about Iraq, with majorities saying they are at least somewhat confident in all the candidates to make the right decisions on Iraq.
Media Treatment Of The Candidates
Voters say the media have been harder on Clinton than on the other presidential candidates. Thirty-one percent of registered voters say the media have been harder on Clinton than the others, while 15 percent feel the media have been hardest on Obama and 14 percent say the same of McCain.
Twenty-eight percent say the media have been easiest on Obama, while just 13 percent say the same of Clinton. Women especially think Clinton has been treated harsher than the other candidates, with 39 percent taking that position.
And thirty-nine percent of African Americans think the media has been hardest on Clinton. Just 24 percent of African Americans say this about Obama.
As for McCain, Republicans are more likely than Democrats to say the media has been harder on him - but still just 19 percent say that.
This poll was conducted among a random sample of 1,067 adults nationwide, interviewed by telephone March 15-18, 2008. The error due to sampling for results based on the entire sample could be plus or minus three percentage points. The error for subgroups is higher. An oversample of African Americans was also conducted for this poll, for a total of 122 interviews among this group and 106 African American registered voters. The results were then weighted in proportion to the racial composition of the adult population in the U.S. Census. The margin of error for African Americans (overall and registered voters) is plus or minus nine percentage points.