Polls showed him as the front-runner until he stumbled by complaining to an interviewer that when he had visited Vietnam, he had been "brainwashed" by military briefers there into supporting the war. That remark generated enough controversy to cost him the nomination.

Some historians suggest more attention might have been paid to Romney's Mormonism if he hadn't torpedoed his own candidacy so early. And in those days, many Christian conservatives were southern Democrats and less interested in GOP primary contests.

Romney withdrew as a presidential candidate on Feb. 28, 1968, just ahead of the March 12 New Hampshire primary won decisively by Republican Richard Nixon.

Mitt Romney supporters point to Kennedy, who overcame questions about his religion to become the first Catholic elected president. He did that, in part, by speaking before Protestant clergymen in Houston in 1960 to dispel fears that, as a Catholic president, he would be subject to direction from the pope.

Can Romney neutralize the religion issue the same way Kennedy did — by giving a major speech explaining the role his Mormon faith plays in his political life?

In an interview in Iowa with The Associated Press, Romney said he's considering dealing with the issue in a comprehensive manner, although "it's probably too early for something like that."

"At some point it's more likely than not, but we'll see how things develop," Romney said.

But Kennedy had one advantage that Romney doesn't. When he ran, Catholics made up roughly 28 percent of the U.S. population. Although one of the fastest growing faiths in the world, Mormons represent less than 2 percent of the U.S. population with 5.5 million members across the country.

"The differences between Kennedy and Romney are in the nose count," said political historian Stephen Hess. "The religion issue may have hurt Kennedy, but it sure helped him at the same time" as Catholics threw their support behind him.

"There is no way that capturing the Mormon vote is going to win Romney anything," Hess said.