Iowa GOP voters see Romney as best challenger to Obama

Paul had the backing of 48 percent of voters under age 30 and nearly as many independents, giving him large leads in both categories. That could be good news for Paul in New Hampshire, where independents represented almost 4 in 10 voters in that state's 2008 GOP presidential primary. Nearly a quarter of Iowa's GOP voters Tuesday were independents, up from 2008, so their proportion in New Hampshire might grow this year as well.

About a third of GOP caucus goers said they were most concerned about budget deficits, and 3 in 10 of them picked Paul, more than any of his rivals.

The survey was conducted for AP and the television networks by Edison Research as voters arrived at 40 randomly selected caucus sites in Iowa.