Of the many disturbing trends for Republicans this campaign season, one of the most troubling is the drop in support among white evangelicals.

The number of conservative Christians with a favorable view of the party has plummeted from 74 percent to 54 percent between 2004 and this year, according to the Pew Research Center for the People & the Press. Evangelicals comprise more than one-third of GOP voters.

But analysts say it's far too soon to write off the powerful Republican-evangelical alliance that helped the party dominate in the 2004 election.

• Click here to visit YOU DECIDE 2006, FOXNews.com's complete election center.

Conservative Christians have been here before — disappointed that Republicans they helped elect failed to enact the evangelical agenda — yet they have consistently returned to the GOP. Even as they question the current Republican leadership, evangelicals are far more supportive than other Americans of President Bush and the party, the Pew Center found.

"There's a lot of discontentment," said Marvin Olasky, editor of the Christian newsweekly World and a framer of the "compassionate conservative" language used by Bush. "But unfortunately for most conservative evangelicals, there's no alternative."

That doesn't mean the GOP can rest easy. Damage over the past two years could cost Republicans on Nov. 7 if disenchanted evangelical voters stay home. And tensions with a core constituency would muddy the run-up to the 2008 presidential race.

Evangelical frustration is apparent in their qualified endorsements of GOP candidates.

James Dobson of Focus on the Family said at a September "Stand for the Family" rally in the battleground state of Pennsylvania that Republicans have made no progress on issues important to Christians who helped put the GOP in control.

Still, he told attendees to vote.

"Whether Republicans deserve the power they were given," Dobson said, "the alternatives are downright frightening."

The complaints are familiar. Through every Republican victory since the Moral Majority was formed in 1979, abortion remained legal, gay couples won greater acceptance and prayer was still barred from public schools.

In 1999, Cal Thomas and Ed Dobson, both veterans of the Moral Majority, examined these failures in their book "Blinded by Might," and concluded that politics was too corrupt to be used to spread Christian morality in America. A few other evangelicals suggested conservative Christians withdraw from politics and focus instead on faith.

The retreat never happened. Between 1999 and 2004, the share of white evangelicals identifying themselves as Republican grew from 39 percent to 49 percent, the Pew Center found.

It's unclear whether this campaign season will be different.

Like many other Americans, evangelicals are upset by U.S. strategy in Iraq, corruption in the Republican-led Congress, and the case of former GOP Rep. Mark Foley, who sent sexually explicit e-mails to pages.

But conservative Christian grievances go further.

Dobson and other evangelicals have accused Congress of ignoring their policy agenda on marriage and abortion. The Bush administration did give evangelicals what they wanted most — conservative U.S. Supreme Court justices — by appointing John Roberts and Samuel Alito.

Yet, even that victory was sullied.

Many evangelicals complained that Bush's pitch to Christians on behalf of his first choice for the seat now held by Alito, Harriet Miers, was based on her conservative Christian faith. Those who considered her unqualified for the post found the approach patronizing.

Disillusionment has led to a backlash. Some evangelicals are once again warning that lawmakers are using Christians for their votes and politics is corrupting the church.

In the book "Tempting Faith, An Inside Story of Political Seduction," author David Kuo, a former aide in the White House faith-based office, wrote that Bush aides privately called conservative Christians "nuts," "ridiculous" and "goofy."

Kuo, a born-again Christian, said Republicans have failed to fulfill campaign promises to evangelicals, yet have kept Christians on their side by portraying Bush as "pastor-in-chief."

"So much of the support for his presidency comes purely on the basis of his Christian faith," Kuo said in a phone interview. "The biblical notion is to defer to your pastor. Christian political leaders have taken advantage of that — portraying themselves as spiritual leaders — but they're not. They're political leaders."

William Martin, author of "With God on Our Side, The Rise of the Religious Right in America," said Kuo's book may have an impact because it touches on the long-standing evangelical sensitivity to being marginalized by broader society.

But Martin said only a small minority of evangelicals believe they should abandon politics — leaving the Republican grip on the movement intact for now.

"The great advantage that conservatives have had within the evangelical community is that a consistent, coherent message has been repeated over and over and over to people who meet together one, two, three times a week," Martin said. "Liberals really have nothing comparable to that."