Should a politician - in a country that separates Church and state - declare his commitment to a religious faith? Or should he be careful to declare that his faith has no bearing on his politics?
It's an interesting question. And it has particular bearing on the American presidential election.
Last week, the well-known American essayist Adam Gopnik castigated Paul Ryan for his open declaration of his Catholic faith, comparing him unfavourably with the late John F Kennedy, who declared that he kept his religion separate from his politics.
Mr Gopnik described Mr Ryan's views as "disturbing" and "scary" after the Republican vice-presidential candidate said: "I don't see how a person can separate their public life from their private life, or from their faith. Our faith informs everything we do."
That, wrote Mr Gopnik, in the New York Times, was "a shocking answer - a mullah's answer, what those scary Iranian 'Ayatollahs' ... say. Ryan was rejecting secularism itself, casually insisting ... that the usual necessary distinction between politics and religion, between state and Church, cannot and should not exist."
This emerged after the discourse touching on abortion between Mr Ryan and Obama's vice-president, Joe Biden, who also happens to be a Catholic, but who does draw a distinction between personal belief and state law. Mr Biden maintains his faith is private and personal and is separate from his respect for the law.
Mr Gopnik recalled, with admiration, how John F Kennedy had set the standard by saying that "faith was faith and public service, public service, each to be kept separate from one another".
But we live in a different time. Mr Kennedy was campaigning in 1960, when America was a much more affirmatively Protestant country, suspicious of the perils of 'interference' from Rome. JFK was at pains to show he would serve America, not the Holy See.
In fact, his values turned out to be hardly an adornment to Catholic, or indeed any Christian, ethics. He not only repeatedly cheated on his wife, but did so with scant respect for the women involved. He and his brother Robert probably caused, at least indirectly, the death of Marilyn Monroe by their callous treatment of her insecure and fragile personality, using her for sex and then dumping her.
The Kennedy values, as transmitted from old Joe Kennedy, were about power, money and always being first.
Whether Mr Ryan will emerge, through history's perspective, as a less-than-admirable character, we cannot yet judge.
We live in a global information age, when it would be a lot more difficult for a politician to sleep with a gangster's moll, or have quick sex with a movie star, than it was in the early-1960s.
But Mr Ryan declares openly what he believes in and so far hasn't been charged with hypocrisy. Many Catholics do not agree with Mr Ryan's advocacy of rugged individualism, his acceptance of the death penalty, his war on welfare and his adulation of Ayn Rand, the capitalist philosopher who believed that the most admirable ideal that drove civilisation was "selfishness" (and the most despicable was charity).
Yet Mr Ryan does seem to be honest and when he says that his faith is part of his values, he is stating the truth, not trying to hide something for the sake of power.
The New Testament directs Christians to separate 'the things that belong to Caesar, and the things that belong to God', which indicates a separation of the secular from the religious.
But in the era of the New Testament, the division between Caesar and God did seem a lot clearer.