The mistaken belief that President Obama was born outside of the United States has persisted among a hard-core segment of the population. In a recent CBS/New York Times poll, 25 percent of the public incorrectly said he was born outside of the United States.

Polling from Gallup/USA Today, Fox News and CNN have found similar levels saying he was born in another country. Obama released his long-form birth certificate on Wednesday.

Partisanship is a key driver in opinions here: in the CBS/NYT poll, as many as 45 percent of Republicans said he was not born in the United States. That number was up 13 percentage points from a similar poll last year. Last April, by 41 to 32 percent, more Republicans said he was born in the United States. That flipped to 45 to 33 percent saying he was born elsewhere in the poll released last week.

Digging deeper into the data reveals that many of the people who doubt his U.S.-paternity only suspect this. Fewer think there is “solid evidence.” In a Washington Post-ABC News poll in April of last year, 20 percent said Obama was not born in the United States. But asked a follow up question, only 9 percent overall said there was solid evidence for this belief. The rest said it was only their suspicion.

This distinction between evidence and suspicion was especially striking among Republicans. Among the 31 percent of Republicans who doubted his place of birth, 19 percent said it was only their suspicion and 11 percent said there was solid evidence.