Texas Gov. Rick Perry (R) is accelerating efforts to explore another White House bid.
Sen. Rand Paul said the failure to beef up security in Libya was a "dereliction of duty."
Forty-four percent of respondents said they would support Clinton; Christie had 34 percent.
Rep. Tammy Duckworth (D-Ill.) is "Ready for Hillary," making her the second House lawmaker to back the group working to draft Hillary Clinton to run for president.
"We are going to beholden to the foreign master,” she said in Iowa.
McCain said he's received "a spate of emails and letters and phone calls" urging him to run.
Democrats insist they can thwart Chris Christie if he seeks the White House in 2016.
The New Jersey governor positioned himself squarely as a Washington outsider.
“Is a conservative in New Jersey a conservative in the rest of the country?” Perry asked.