WASHINGTON -- At the moment, Barack Obama is winning a smaller share of Democrats than John Kerry did on Election Day four years ago. Yet Obama is beating John McCain by six points in the latest Gallup Poll. How can this be?

For all the talk this year about bipartisanship, a sharp shift in partisan loyalties toward the Democrats, visible in a series of polls this week, could prove to be the defining fact about the 2008 election.

In a report released Thursday, Gallup found that where McCain was winning 85 percent among self-identified Republicans, Obama was winning only 78 percent of Democrats.

Yet Obama led McCain in the June 5-10 survey, 48 percent to 42 percent. Obama enjoyed a seven-point advantage among independents, but Gallup noted that even if independents were excluded from the analysis, Obama still had a five-point lead because Democrats now outnumber Republicans 37 percent to 28 percent. When independents are asked their partisan leanings, the Democratic advantage reaches 13 points.

In the 2004 election, John Kerry carried 89 percent of the vote among self-identified Democrats, according to the network exit poll, but Democrats and Republicans accounted for an equal share of the electorate. President Bush won with an even larger share (93 percent) among supporters of his own party.

David Winston, a Republican pollster, acknowledges his party's problems, but is skeptical about large changes in party identification. He notes that while polls have often reported significant shifts in party loyalties during the course of campaigns, the gap between the two parties historically narrows by Election Day. Independents, who turned on the GOP in 2006, remain the key to this year's outcome, he said.

The good news for McCain is that he has consistently run ahead of his party this year. The bad news is that the GOP is in such a deep hole that McCain may not be able to climb out. When voters in a new NBC News/Wall Street Journal poll were asked, without candidates' names, which party they wanted in the White House, Democrats had a 16-point lead. But when they were asked to choose between Obama and McCain, Obama led by only 6 points.

Geoff Garin, a Democratic pollster who worked for Hillary Clinton's campaign this year, sees evidence for a realignment in a steady move of middle-income voters toward the Democrats. "Identification with the Democrats has crept up among voters in the $50,000- to $75,000-a-year range and is now moving up beyond that," partly in response to "the pain of the Bush economy."

The paradox is that sharp shifts in partisan identification often presage periods of bipartisanship. If Obama were to win because of the country's Democratic tilt, moderate Republicans in Congress could move his way to protect themselves against a Democratic tide. A comparable shift of worried Democrats helped Ronald Reagan build bipartisan majorities for his tax and budget programs in 1981. "There really is the potential for Barack Obama to build coalitions with Republicans in the middle -- if there are Republicans left in the middle," said Garin.

Even in the currently fractious Congress, such defections have already created bipartisan majorities for Democratic measures. In Thursday's House vote to extend unemployment benefits by 13 weeks, 49 Republicans broke with President Bush to support the measure and give it a veto-proof majority.

The realigning mood took concrete form this week in Virginia when two prominent Republicans, Vincent Callahan, former chairman of the state House Appropriations Committee, and John Chichester, former state Senate president, endorsed Democrat Mark Warner for the U.S. Senate. Callahan said he was "extremely distressed" by the condition of Virginia's GOP, adding that it risked becoming "a minority debating society."

Other signs of the party shift include the NBC/Journal poll's finding that voters preferred a Democratic Congress to a Republican Congress, 52 percent to 33 percent, even though 79 percent disapprove of Congress itself.

Alex Castellanos, a Republican consultant, says that given the Democrats' large advantages, "this should be one of Obama's high-water marks, and he's not there."

But he acknowledges that to win back the ground his party has lost, it needs a new approach to governing and cannot simply continue to run against government. "We have trapped ourselves in this world where we believe we either have to be faithful to our principles, or we have to govern," he said. "It's a recipe for not governing." That is the trap McCain needs to escape.


E.J. Dionne, Jr. is the author of the recently published Souled Out: Reclaiming Faith and Politics After the Religious Right. He is a Washington Post columnist, a senior fellow at the Brookings Institution, and a professor at Georgetown University.

By E.J. Dionne Jr.