Republican candidate Mitt Romney's religion has finally become a subject of public discussion in the race for the U.S. presidential nomination, with accusations flying over the weekend that his Mormon religion is actually a cult.

Many observers of the U.S. race have watched and waited, expecting the "M" card to make an appearance as candidates struggle to galvanize their support.

It happened Friday at a conservative conference in Washington D.C. when mega-church pastor Robert Jeffress, who introduced Texas Gov. Rick Perry, said Mormonism is a cult and true Christians should only vote for Perry.

During his introductory comments at the Values Voters Summit of Christian Conservatives Jeffress said Perry was "a brilliant leader, a true conservative, and he is a genuine follower of Jesus Christ."

That caused many to question whether he was inferring that Romney, by contrast, wasn't a true Christian. Speaking to reporters afterwards, Jeffress confirmed that that indeed was his meaning.

"In my estimation Mormonism is a cult and it would give credence to a cult to have a Mormon candidate," he said.

He added that Romney is a "good, moral person with a wonderful family," but said that in itself doesn't make him a Christian.

"Every true born-again follower of Christ ought to embrace a Christian over a non-Christian," Jeffress said.

Romney and Jon Huntsman, another candidate for the Republican nomination, are both Mormons.

Romney and Perry are considered the frontrunners in the race and Perry, who is trailing slightly behind Romney, could see a bump in the polls if the question of Romney's religion gains traction.

A recent poll found that one in five U.S. voters would support a Christian candidate over a Mormon.

After the comments emerged over the weekend, Perry's campaign team told ABC News that the governor didn't believe Mormonism was a cult.

Romney himself, speaking on Saturday, told a group that "poisonous language doesn't advance our cause. It's never softened a single heart not changed a single mind," though he didn't directly link his comments to Jeffress' remarks.

Romney called on Republicans to focus on the "conservative beliefs and values that unite us" rather than the issues that sow division.

Other candidates attempted to avoid the thorny debate over Mormonism and Christianity altogether.

Candidate Herman Cain was pressed on the matter, and refused to wade into the debate or share his opinion about whether Romney is in fact a Christian.

Michele Bachmann, a Minnesota congresswoman, also avoided the topic on Sunday, refusing to answer when asked if Romney is a Christian.

On Monday, Perry's campaign ignored the subject of religion but did release a television ad slamming Romney over his stance on health care and flip-flopping on key issues.

The winner of the Republican nomination race will take on Barack Obama in next November's election.

Perry had surged to an early lead after he entered the race in August, but has slipped back in the polls after a number of poor debate performances, and is now slightly behind Romney.