WASHINGTON » It’s the conspiracy theory that won’t go away. And it’s forcing Republican officials and presidential contenders to pick sides: Do they think Barack Obama was born outside the United States and disqualified to be president?

As the Republican candidates tiptoe through the mine field, Democrats are watching. They hope the debate will fire up their liberal base and perhaps tie the eventual GOP nominee to fringe beliefs that swing voters will reject.

In recent days several prominent Republicans have distanced themselves, with varying degrees of emphasis, from the false claim that Obama was born in a foreign country. But with a new poll showing that two-thirds of adult Republicans either embrace the claim or are open to it, nearly all these GOP leaders are not calling for a broader effort to stamp out the allegations.

"It’s a real challenge for the Republican Party and virtually every Republican candidate for president," contends Democratic pollster Geoff Garin. If it’s not handled well, he said, all-important independent voters might see Republicans as extreme or irrelevant.

Many Americans consider claims of Obama’s foreign birth to be preposterous, unworthy of serious debate. Yet the "birther" issue threatens to overshadow the early stages of the GOP effort to choose a presidential nominee for 2012. Real estate mogul Donald Trump has stirred the pot lately, repeatedly saying Obama should provide his original birth certificate.

From a political standpoint, it’s impossible to dismiss the matter as conspiratorial fantasy, akin to, say, claims that the 1969 moon landing was staged. In the latest New York Times-CBS News poll, 45 percent of adult Republicans said they believe Obama was born in another country, and 22 percent said they don’t know. One-third of Republicans said they believe the president is native born.

The same poll a year ago found considerably less suspicion among Republicans. A plurality of GOP adults then said Obama was U.S.-born, and 32 percent said they believed he was foreign-born.

In the latest poll, about half of all independents said Obama was born in the United States. The other independents were about evenly split between those saying he is foreign-born, and those saying they don’t know.

Ten percent of Democrats said Obama was born overseas, and 9 percent were unsure.

Obama’s birth certificate indicates he was born in Hawaii in 1961. Newspaper birth announcements at the time reported the birth, and news organizations’ investigations have rebutted the birthers’ claims. The Constitution says a president must be a "natural born citizen."

Trump’s leap to the top tier of potential GOP presidential contenders in recent polls has frustrated party leaders who’d like the birthplace issue to go away.

The House’s top Republicans —Speaker John Boehner and Majority Leader Eric Cantor — say they are satisfied that Obama was born in Hawaii. But they have declined to criticize those who state otherwise, and Boehner has said it’s not his job to tell Americans what to think.

Trump, meanwhile, keeps fueling the fire. Even though many people doubt he will run for president, he has forced other Republicans to take stands.

Former Massachusetts Gov. Mitt Romney and former Sen. Rick Santorum of Pennsylvania have been the most direct in rejecting the birthers’ claims. "I believe the president was born in the United States," Romney told CNBC.

Santorum has no doubt that Obama was born in Hawaii, and he "believes this debate distracts us from the real issues," said his spokeswoman, Virginia Davis.

Mississippi Gov. Haley Barbour accepts the president’s word about his birthplace, his staff said.

Former Minnesota Gov. Tim Pawlenty told an Iowa audience, "I’m not one to question the authenticity of Barack Obama’s birth certificate." He added a little jab: "When you look at his policies, I do question what planet he’s from."

When ABC’s George Stephanopoulos showed a copy of Obama’s birth certificate to Rep. Michele Bachmann of Minnesota, who was ambivalent at first, she said: "Well, then, that should settle it. … I take the president at his word."

Former vice presidential nominee Sarah Palin gave mixed signals in a recent Fox News appearance. She praised Trump for "paying for researchers" to dig into claims of Obama’s foreign birth. But she added, "I think that he was born in Hawaii because there was a birth announcement put in the newspaper."

Former Arkansas Gov. Mike Huckabee has dismissed claims that Obama is foreign-born, calling them a distraction. But on a February radio show, Huckabee referred to Obama "having grown up in Kenya," the birthplace of the president’s father.

Obama grew up in Hawaii and Indonesia. A spokesman said Huckabee’s statement was simply a mistake.

Aides to former House Speaker Newt Gingrich said voters have not asked him about the birthplace question and he has not discussed it.

The issue has spread to several states where Republican-controlled legislatures have introduced or passed bills requiring presidential candidates, and sometimes others, to prove their citizenship. Arizona Gov. Jan Brewer, a Republican, recently vetoed such a bill, calling it "a bridge too far."

Democrats think the birthplace issue might fire up liberals, especially minorities, who in many cases have been dispirited by Obama’s frequent compromises with conservatives to pass legislation. Blacks who embraced Obama’s barrier-breaking election now see some Republicans claiming he has no constitutional right to be president.

The New York Times-CBS poll was worded in a way that might have subtly encouraged respondents to say Obama is foreign born. "Some people say Barack Obama was NOT born in the United States," the poll’s callers said, but they did not offer counter arguments.

Moreover, some pollsters think respondents will seize a chance to call Obama a Muslim or non-citizen to convey something else: a dislike for him or his policies.

"Some people who strongly oppose a person or proposition will take virtually any opportunity to express that antipathy," writes Gary Langer, who polls for ABC News.

Garin, the Democratic pollster, doesn’t buy it in this case. The birthers’ claims are so prevalent, especially on conservative TV and radio shows, he said, that poll respondents are likely to say what they truly believe about a much-discussed topic. 

"There are high- profile people, including Donald Trump and many others in the conservative media, who advocate and validate this point of view each and every day," Garin said. The big question about the birthplace issue, he said, "is the extent to which it drives a wedge within the Republican Party" and turns off independents in November 2012.