When President Bush campaigned for reelection three years ago, this community near Denver was a promising territory: a fast-growing collection of cul-de-sacs and nearly identical homes, where thousands of young families seemed open to Republican ideas.

The "exurbs," the far-flung suburbs of Minneapolis, Cincinnati, Denver and other cities, were full of parents too busy with school, church and work to bother affiliating with either major party. GOP strategy held that, come election time, Republicans could win these voters with talk of lower taxes, stronger security and family values -- not only to help Bush, but to position the party for long-term dominance.

But talk today to Donna Howe, 49, a mother of two who backed Bush in 2004, and a dramatic setback to that plan emerges.

Like many of her neighbors, Howe is an independent voter who is frustrated by the direction of the country, nervous about national security -- and open to a Democratic candidate "with good ideas on healthcare and a reasonable plan to deal with the Iraq war."

The same holds for Jim Tuccio, 44, who lives a few streets away and blames Republican mismanagement of the economy for strangling the mortgage company he once worked for, costing him his job.

Unaffiliated voters, who split evenly between Bush and Democrat John F. Kerry in 2004, are now looking more favorably at the Democratic Party, a reaction to Bush's slide in the polls, the U.S. struggle in Iraq and other disappointments with GOP leadership.

It is a dramatic political development in such a closely divided electorate, and one that is likely to paint a different Electoral College map that for the last two elections was shaded Republican red in the heartland and the South, and Democratic blue in the coastal West, the Upper Midwest and the Northeast.

Strategists in both major parties believe the shift among independents was crucial to last year's Democratic sweep of congressional and state races in a number of traditionally Republican states, such as Colorado, Missouri, Montana and Ohio.

Here in Douglas County, the state's Democratic governor won nearly 50% of the vote last year -- a major achievement, considering that fewer than one in five voters here are Democrats and that President Bush had won overwhelmingly in 2000 and 2004.

Strategists agree that the shift foreshadows a far more complicated calculus as next year's presidential election unfolds. Already, both major parties are examining ways to lure the increasingly important constituency, which though losing faith in Bush, is not enthusiastic about the Democratic Party. At stake are the White House and control of Congress, with competitive Senate races expected in Colorado as well as in Maine, Minnesota, New Hampshire and Virginia -- all with heavy concentrations of independent voters.

"These independents are not marching into the Democratic Party and declaring themselves Democrats, but the change is in the tilt," said Carroll Doherty, associate director of the Pew Research Center for the People & the Press. "They are definitely leaning toward the Democrats."

Polls show that the movement among independents is a broad phenomenon.

Surveys by Pew have found that far fewer voters now identify with the Republican Party. Where the two parties had roughly an equal hold on the electorate in 2002, now only about 35% call themselves Republicans or independents leaning toward the GOP, compared with about 50% aligning with the Democrats.

Moreover, independent voters are shifting their outlook on government, Pew found, putting them more in line with the Democratic Party in their concern about income inequality and belief in a government safety net for the poor.

Even some of the GOP's most ardent backers -- supporters whom Bush's campaign courted heavily in 2004 -- are less enthusiastic about the party, among them Latinos and women in suburbs and exurbs.

And holding the loyalty of evangelical Christians has become one of the most surprising problems for the Republican Party.

Support among white evangelicals neared 100% after the Sept. 11 terrorist attacks, and the White House used pastors, church membership directories and other tools to mobilize evangelicals for the 2004 election. But Bush's support among these voters dropped to 44% in a June Pew survey, sparking concern in GOP circles that an unmotivated base would cripple the party's efforts to compensate for losses among independent voters.

Phil and Sue Waters helped organize their suburban Denver megachurch to campaign for an anti-gay-marriage referendum on last year's state ballot. But even these core GOP voters are feeling less excited about pitching in for the party's candidates in 2008.

Their church, Faith Bible Chapel in Arvada, has long been a hub for Republican politics in closely fought Jefferson County. In a surprising change last year, a Democrat won the area's congressional seat. Democrats plan to target the county next year for the open Senate seat as well as the presidential election.