"Obama now virtually tied with Clinton, poll shows" (UPDATED)

UPDATE: Jonathan Singer on MyDD provides some analyis of this poll (excerpt):

Jerome is definitely correct in writing that any campaign that relies to heavily on the support of Independents could crumble as voters unaffiliated with the Democratic Party cannot always participate in nominating contests and Independents are less likely to turn out for a Democratic Primary than Democrats. Nonetheless, if Obama -- or another candidate, for that matter -- can run up a major lead among Independent voters and turn them out in the states where they can participate (particularly in New Hampshire), there is a potential that this voting clique can in fact play an oversized role in picking the next Democratic nominee.

USA Today:

WASHINGTON — Hillary Rodham Clinton and Barack Obama are essentially tied for the Democratic presidential nomination, according to a USA TODAY/Gallup Poll, the first time that the New York senator hasn't clearly led the field.

POLL RESULTS: Which candidate do most lean towards?

The Illinois senator bests Clinton by a single percentage point, 30%-29%, if the contest includes former vice president Al Gore.

Clinton bests Obama by a single point, 37%-36%, if it doesn't include Gore.

The survey of 310 Democrats and 160 independents who "lean" Democratic, taken Friday through Sunday, has a margin of error of +/- 5 percentage points.

FIND MORE STORIES IN: Democrats | Republican | Al Gore | Poll | Hillary Rodham Clinton | NH | Barack Obama | Presidential candidates

National polls taken the year before an election are "clearly not a prediction of how they're going to end up," cautions political scientist Charles Franklin of the University of Wisconsin. "On the other hand, the national trends are a good indicator of whose messages are beginning to work and whose messages may be falling short."

No other major national poll has shown the Democratic race so close. An ABC News/Washington Post poll taken last Tuesday through Friday gave Clinton a 12-point lead.

Mark Penn, Clinton's chief strategist, calls the USA TODAY poll "an outlier" that is "completely out of sync" with other surveys. He says it is "seriously flawed" for including so many independents unlikely to vote in Democratic primaries.

"National polls are not all that relevant in a process that is largely sequential" through early contests in a series of particular states, says David Axelrod, Obama's chief strategist.

Even so, Axelrod adds, "This poll is consistent with what we see on the ground" as increasingly huge crowds show up for Obama's appearances. He says it also undercuts the argument Clinton strategists have tried to make that "she's an [unconquerable] Juggernaut."

Among Democrats alone, Clinton leads Obama by 5 points, 34%-29%. That's a significant narrowing from the USA TODAY poll taken in mid-May, when she led by 17 points. Among independents, Obama leads by 9 points, 31%-22%.