President Obama is taking an interesting approach to the “birthers” and others who continue to falsely suggest he was not born in the United States: humor.

On Thursday, the same day that Donald Trump, who is weighing a 2012 Republican presidential run, said he had some "doubt" Obama was born in Hawaii, the president did a long riff on the issue at a St. Patrick’s Day event on Capitol Hill.

“Speaking of ancestry, there has been some controversy about my own background,” he said at the “Friends of Ireland” luncheon. “Two years into my presidency, some are still bent on peddling rumors about my origins. So today I want to put all those rumors to rest. It is true my great-great-great-grandfather really was from Ireland. It’s true. Moneygall, to be precise. I can’t believe I have to keep pointing this out.”

A few days earlier, at the Gridiron Dinner, he joked that “some things just bear repeating” as the Marine band played the Bruce Springsteen song “Born in the USA.”

But the jokes are an attempt to poke fun at a rather serious subject: A CNN poll last year showed a quarter of Americans, mainly Republicans, had some doubts about Obama’s birthplace.

Those doubts have persisted despite the Obama ’08 campaign’s “Fight the Smears” Web site, which debunked the birthplace stories and other falsehoods about the president’s background, and also despite Obama’s numerous references to his childhood in Hawaii and his annual trips there.

But the intensity of the birthers is likely to be a dynamic of the 2012 campaign. Trump and others flirting with running for president on the Republican ticket are making these references to Obama’s background in part because doing so appeals to conservative activists.

And Obama, too, seems aware the gambit is not going away.

“There’s no weakness in us trying to reach out and seeing if we can find common ground” with Republicans, he said at a Democratic fundraiser in Boston earlier this month. But he added: “Now, there are going to be times where we can’t. I was born in Hawaii, what can I say? I mean, I can’t change those facts.”

Obama today

The president will head to Brazil late Friday for a four-day, three-country trip that will also include stops in El Salvador and Chile. He is also expected this afternoon to make a statement about Libya, a day after the U.N. Security Council authorized military action there.