Nearly half of Republican voters in Iowa said they don't think President Barack Obama was born in the United States, but despite the large "birther" presence in the state, many had negative views of real estate mogul Donald Trump.

Forty-eight percent of Iowa Republicans said they don’t believe that Obama was born in the United States, according to a survey by the left-leaning Public Policy Polling. Another 26 percent said they weren’t sure.

Trump, a potential Republican presidential candidate, has been courting the media's attention by questioning Obama's eligibility to be president. He first revealed he had some doubts that Obama was a U.S. citizen during an interview with ABC News' Ashleigh Banfield in March.

Later appearing on Fox News, he claimed that the president has not provided his birth certificate and suggested that Obama has "spent millions" trying to avoid the question.

The president was born in the state of Hawaii and released a certificate of live birth to prove it in June 2008.

Although Trump could be the "birthers'" candidate of choice, he was the most disliked candidate among Republican voters in Iowa, with 41 percent saying they had a positive view of him and a nearly equal amount, 40 percent, saying they had a negative view of him.

Public Policy Polling also found a significant birther presence in New Hampshire, where 42 percent of Republican voters do not believe Obama is a citizen.

Many of the so-called "birthers," such as American Independent Party presidential candidate Alan Keyes, believe there is persuasive evidence that Obama was born in Kenya in 1961 and that his birth certificate was faked in order to make him eligible for the Presidency.

A lawsuit by Keyes that claimed Obama is not eligible to occupy the White House because he is not a natural born citizen was thrown out by the Third District Court of Appeals in October. Last year, a district court judge dismissed a similar lawsuit filed by Orly Taitz, who was fined $20,000 for "wasting judicial resources" with her "frivolous" lawsuits.