President Obama addresses the press corps Wednesday in the White House breifing room. The White House released a long form version of his birth certificate earlier that morning. (Brendan Smialowski/GETTY IMAGES)

After refusing for more than two years to indulge the most corrosive of conspiracy theories questioning his legitimacy, President Obama finally decided that he’d had enough.

He was frustrated and annoyed that questions about where he was born — once the province of the political fringe and more recently fanned by showman and real estate mogul Donald Trump — had arisen even in an interview last week with ABC News anchor George Stephanopoulos.

The “birther” question had become a distraction, one that was getting in Obama’s way as he tried to sell the country on his approach to long-term deficit reduction.

On April 19, Obama ordered White House counsel Robert Bauer to find out what it would take to retrieve a longer and more detailed version of his Hawaiian birth certificate, a document not routinely released by state authorities.

That set into motion several days of intense, secret maneuvering that culminated in an extraordinary moment Wednesday. The president appeared in the White House briefing room with evidence that he had indeed been born in the United States, as the Constitution requires.

In a six-minute statement, Obama alternately poked fun at the “sideshows and carnival barkers” that had made such a declaration necessary and pleaded for the media and political world to focus on the serious challenges that face the nation.

“We do not have time for this silliness,” Obama said. “We’ve got better stuff to do. I’ve got better stuff to do. We’ve got big problems to solve.”

Some of the president’s conservative critics have pushed the theory that Obama, whose father was Kenyan, was born in Africa, as a way to question his constitutional legitimacy and even his basic American-ness. It is a falsehood that has gained remarkable currency. The most recent CBS/New York Times poll suggests that about a quarter of Americans believe it to be true. Among Republicans, 45 percent said they think Obama was not born in the United States.

The overall number has risen by five percentage points over the past year — driven largely by a 13-point uptick among Republicans. Among independents, the number has remained steady, around one-quarter.

Even before the White House procured a copy of the complete document and posted it on the Internet, there was ample evidence that Obama had indeed been born in Hawaii nearly two years after it became a state. During the 2008 campaign, he produced the standard version of his birth record, and newspaper birth announcements at the time corroborated it. Some 70 lawsuits challenging Obama’s birthplace have been dismissed by various courts.

Innuendo, of course, has always hung around backstage in politics — and the general rule has always been that the best way to handle it is to ignore it.

“Rumor travels faster,” the humorist Will Rogers observed nearly a century ago, “but it don’t stay put as long as truth.”

But today’s is a brutal, instantaneous media culture. Obama — the nation’s first African American president, and one who was raised in multicultural surroundings — has been the target of toxic, sometimes incongruous rumors.

During the 2008 campaign, he simultaneously battled criticism over his membership in a Christian church with a controversial pastor and murky tales that he was secretly a Muslim. At first, his attitude as a candidate was to stay above the fray; he decided to reverse course when his wife, Michelle, was falsely accused of using a racial epithet against whites. At that point, Obama ordered the launch of a Web site titled “Fight the Smears.”

“Using these as teachable moments, as he did in 2008, has served him well,” said Anita Dunn, who managed Obama’s counterattacks during his campaign and who later served as his White House communications director.

A similar instinct drove Obama’s decision last week to confront the speculation, aides said.

“The President believed the distraction over his birth certificate wasn’t good for the country,” White House communications director Dan Pfeiffer wrote in a blog post on the White House Web site. “It may have been good politics and good TV, but it was bad for the American people and distracting from the many challenges we face as a country.”

Obama told donors in New York on Wednesday night: “Part of what happened this morning was me trying to remind the press and trying to remind both parties that what we do in politics is not a reality show. It’s serious.”

On Friday, Obama signed a letter to Hawaii officials requesting the document, which they replied could be made available Monday. Obama dispatched his outside counsel, Judy Corley, to Hawaii to retrieve it, and she delivered it to the White House on Tuesday night.

The timing for Obama’s appearance was in some ways surprising. It came on a day when the top story might otherwise have been news of changes in the administration’s national security team. White House officials said they wanted to release the paperwork as quickly as possible after receiving it, to preempt any further conspiracies about whether it was doctored. They were also aiming for an element of surprise, catching off-guard a White House press corps that never had any hint that the administration might make this move.

The president told reporters that he wanted the nation to return to serious business; hours later, he left the White House to travel to Chicago, where he taped an appearance on “The Oprah Winfrey Show,” and then to New York for three fundraisers.

Obama’s announcement came just as Trump was arriving in New Hampshire on what was billed as a prelude to a possible run for the 2012 GOP presidential nomination.

Trump has vaulted in some opinion polls regarding the Republican 2012 field, in part by questioning Obama’s birthplace, but a series of major Republican figures, including former Massachusetts governor Mitt Romney, a likely contender for the GOP nomination, and Karl Rove, the top political strategist for President George W. Bush, have publicly urged members of the party to move on from the “birther” issue.

Indeed, the controversy carries some measure of political opportunity for Obama. The president has been mentioning the birthers during recent campaign speeches, attempting to fire up his supporters by reminding them of the opposition the president faces.

It “creates, I think, a problem for them when they want to actually run in a general election where most people feel pretty confident the president was born where he says he was, in Hawaii,” Obama said in the ABC News interview. “He doesn’t have horns. We may disagree with him on some issues, and we may wish that, you know, the unemployment rate was coming down faster, and we want to know his plan on gas prices.

“But we’re not really worrying about conspiracy theories or birth certificates,” Obama said, “and so I think it presents a problem for them.”

Staff writer Perry Bacon Jr. and polling manager Peyton M. Craighill contributed to this report.