Huckabee issued a statement Tuesday night that didn't apologize for the remarks but said they were neither approved nor condoned by his campaign. He said he was glad that the supporter had issued his own apology and clarification.
The supporter, a pastor in Windsor Heights, Iowa, had sent an e-mail to Brownback supporters pointing out that Huckabee is an evangelical Protestant and Brownback is not. Huckabee, a former Arkansas governor, is an ordained Baptist minister.
"I know Senator Brownback converted to Roman Catholicism in 2002," Rev. Tim Rude, pastor of Walnut Creek Community Church, wrote in the e-mail. "Frankly, as a recovering Catholic myself, that is all I need to know about his discernment when compared to the governor's."
In the e-mail, Rude calls Huckabee "one of us."
Evangelical Protestants have a history of suspicion toward Catholics, although it has lessened significantly in the decades since the National Association of Evangelicals warned against electing John F. Kennedy, a Catholic, to the presidency in 1960.
Issues such as abortion have brought the faiths closer, although some suspicion remains.
Rude apologized Tuesday, saying he never meant to sound critical of Catholicism.
"I was careless in the first place with my words," Rude said in a statement. "I frankly agree theologically more with a Southern Baptist. In no way do I think a Catholic would not make a great president. In fact, if Governor Huckabee drops out of the race, I will support Senator Brownback."
Brownback, a Methodist until he converted, said through a spokesman that Huckabee should apologize. With days to go before the Aug. 11 Iowa straw poll, a traditional measure of strength, Brownback's campaign has sparred with several other campaigns.
"Governor Huckabee should apologize and denounce this prejudiced whisper campaign," Brownback spokesman John Rankin said. "Political campaigns should focus on the issues that Americans care about, not make bigoted slurs aimed at a person's faith and character."
Huckabee spokesman Eric Woolson said Rude is not a campaign staffer and was expressing a personal opinion in what he believed was a private e-mail.
Huckabee's statement Tuesday night contended that his campaign had the support of Catholics as well as other people of faith.
"I consider Sam Brownback a Christian brother and know that he feels likewise toward me," he said. "Like Senator Brownback, several key members of my staff are Roman Catholic. As believers, we don't have time to fight each other. We need to focus on having a servant's spirit and bringing hope to those who have given up."