WASHINGTON (CNN) -- Former Alaska Sen. Mike Gravel, a Democratic presidential hopeful, told CNN Monday any candidate who voted for the Iraq war is not fit to be president.

"I do not feel that a person who voted for the war -- because that's a judgment call -- is qualified to be President of the United States," Gravel told CNN's Wolf Blitzer. "Fifty million Americans made an opposite decision."

Gravel also predicted he "will be the nominee," when asked if he would support Sen. Hillary Clinton, should the New York Democrat win the party's nomination

Asked to clarify his remark at last week's Democratic debate in South Carolina that several of the Democratic candidates "frighten" him, Gravel said he thinks several are open to the possibility of using nuclear weapons against Iran.

"They have all made statements with respect to Iran that everything is on the table," he said. "That's code for nukes."