So it turns out that Rev Robert Jeffress -- supporter and mentor of US presidential candidate Rick Perry -- doesn't just have a problem with Mormons. He's an equal opportunities hater. In a rant about Catholicism on his radio station last September he unleashed the C-word -- clearly a favourite of his -- calling the church to which a quarter of Americans belong "that cult-like pagan religion" and claiming that it derived from ancient Babylonian mysteries rather than "God's Word". "Isn't that the genius of Satan?" he asked. Not just a cult, then. A Satanic cult. And, for good measure, "a fake religion" too.

This revelation has the potential to cause even more trouble for Perry than the Mormonism row that has rumbled on for almost a week. Bill Donohue, who leads the Catholic League, called on Perry to reject Jeffress and his endorsement - something the candidate declined to do when challenged by Mitt Romney during a TV debate on Tuesday. Donohue called Jeffress "a poster boy for hatred, not Christianity".

In the last presidential campaign, Sarah Palin was forced to distance herself from an African pastor who pursued unconventional sideline as a witch-finder, while Barack Obama was put an in embarrassing position when footage emerged of his pastor, Rev Jeremiah Wright, saying "God damn America!" So the Jeffress row isn't unprecedented. Indeed, Donohue himself was involved in a controversy uncannily similar to the Jeffress/Perry imbroglio early in 2008.

It was Donohue's intervention that persuaded John McCain -- then the Republican front-runner -- to reject the endorsement of an Evangelical pastor named John Hagee. Like Jeffress, Hagee ran a Texas megachurch, and his views about Catholicism were just an uncompromisingly Paisleyite. He referred to it as "the great whore" that "drank the blood of the Jewish people". Doubtless there are parts of Texas where that kind of talk still goes down well. Hagee said other embarrassing things too, for example that Hurricane Katrina was divine punishment for "a homosexual parade" that had taken place in New Orleans shortly before.

McCain expressed himself "glad to have his endorsement" even after Hagee's remarks became publicly known. For McCain, who lacked credibility with the religious Right, having a prominent Evangelical fundamentalist in his camp was an important electoral asset, especially when facing a strong challenge from the former Baptist preacher Mick Huckabee. Until suddenly it wasn't.

So far, while distancing himself from the pastor's expressed view of Mormonism, Perry has made it clear that he still "respects" Jeffress and accepts his endorsement. A Perry spokesman went so far as to accuse Romney of "playing a game of deflection" in making anti-Mormon bigotry a campaign issue. Donohue's challenge may prove less easy to bat aside.

If that wasn't bad enough, a pro-secularism group, Americans United for the Separation of Church and State, has complained to the IRS about Jeffress' use of his official church website to host videos supporting Perry's candidacy.The group claims that this constitutes an abuse of the church's tax-exempt status.

The "pastor problem" is a peculiar feature of modern US politics. Obama's relationship with Wright was long-standing, but other unhelpful endorsements look to be the result of carelessness on the part of candidates. It should not have been difficult for Perry's advisers to discover the hardline views previously expressed by Robert Jeffress about Mormonism, Catholicism, homosexuality and other sensitive issues, or to foresee that they might pose a problem outside those parts of the Southern States that have never mentally left the 17th century.

Given that a successful presidential campaign now seems to require that the candidate be endorsed by prominent, self-appointed, publicity-seeking Christian ministers (or at the very least, such endorsement is perceived to confer a distinct advantage) one would expect that they would be carefully vetted before being allowed to stand on stage and introduce someone-or-other The Next President Of The United States. But this doesn't seem to happen. Instead, it always comes as a great surprise to the candidate when a clip surfaces on YouTube of the pastor concerned saying something outrageous. Strange.