THE relationship between religion and American diplomacy has never been simple. People who cherish America’s church-state separation like to cite the Tripoli treaty of 1797 between America and the Muslim overlords of North Africa, which assured them that “the government of the USA is not in any sense founded on the Christian religion” and pledged respect for Islam.

Conservative American Christians retort that despite that pact, their country went on to fight two tough wars against those Muslim rulers, who were a threat to American merchant ships—though of course religion may not have been a factor.

John Foster Dulles, who ran American diplomacy during the 1950s, as the cold war developed, was descended from Presbyterian ministers and missionaries. But there was no obvious sign that this background influenced his policies. In recent times, it was a Democratic and not-very-religious secretary of state, John Kerry, who acknowledged the spiritual by creating an Office of Religion and Global Affairs to help American diplomats engage with faith leaders. Rex Tillerson, who oversaw the state department until his dismissal a few days ago, disappointed some faith advocates by announcing last year he was downgrading that office by merging it with one that monitors religious freedom.

In practice, the diplomacy practised by a global power has to engage with the world’s messy realities. That means that it cannot pretend religion does not matter, nor can it usefully subordinate its own interests to any particular religious agenda. Expediency tends to prevail. For all his reputed hostility to Islam, even President Donald Trump last year praised the rulers of Saudi Arabia for hosting “the holiest places of one of the world’s great faiths”. He must have been hoping his evangelical supporters were not listening.

Still, even in a Washington, DC, that is used to rude shocks, news of the president’s choice to succeed Mr Tillerson was met with some alarm. Mike Pompeo, who has hitherto been serving the president as head of the CIA, is a zealous, evangelical Christian accused of Islamophobia.

Even among broadly conservative watchers of American foreign policy, there is worry that Mr Pompeo’s apparent sectarian sentiment might be a problem. In the words of Robert D. Kaplan, a veteran global-affairs writer, Mr Pompeo “emblemises an increasingly theological bent in American politics, and in particular in a strand of American conservatism.” This contrasted with earlier eras when “American leaders were often churchgoers but their governing spirit was refreshingly secular.”

As is noted by Shadi Hamid, a senior fellow of the Brookings Institution think-tank, Mr Pompeo comes across as an educated person whose negative ideas about Islam are more thought-through, and hence perhaps more worrisome, than the “visceral, almost incoherent” suspicion of that faith which Mr Trump exuded as a candidate. “It is not a good thing when the public face of American diplomacy holds views which demean an entire religion,” says Mr Hamid.

Several things have earned Mr Pompeo the reputation of being a kind of latter-day Crusader. One is a video clip in which he argues vigorously that at least some individuals are motivated by their Muslim beliefs, and by things they read in the Koran, to commit terrible violence. Watched closely, the video does not show him to believe that all Muslims think that way. What is more striking is the remedy of Christian solidarity he proposes: Islam-inspired terrorists “will continue to press against us until we make sure…we know that Jesus Christ is the only solution for our world.”

There is also concern about Mr Pompeo’s reaction to the bomb attack on the Boston marathon in 2013. As a Congressman, he said Muslim leaders who failed to condemn the outrage, and to call it incompatible with Muhammad’s teaching, were “potentially complicit”. Arsalan Iftikhar, a writer and lawyer who helps run an anti-Islamophobia programme at Georgetown University, was one of many Muslim-Americans who found those comments insulting to leaders of Islam in America, who used all their authority to excoriate the bombing.

For Mr Iftikhar and others, yet another worry about Mr Pompeo’s record in Congress is the campaign he waged to have the global Islamist movement known as the Muslim Brotherhoodformally designated as a terrorist organisation. As is noted by Khaled Beynoud, an associate law professor at University of Detroit Mercy, there is a widespread fear among Muslim-Americans that such a designation would lead to the banning of civil-society groups in America which lobby peacefully against discrimination, on the grounds that they are tainted by alleged links with the Brotherhood.

As it turns out, designating the Brotherhood as a terror group is a policy option the Trump administration has considered but so far stopped short of taking. It has been reported that CIA professionals are among those who oppose the move; so whatever he now thinks, Mr Pompeo will at least have heard all the counter-arguments at his previous work-place.

On all these matters, Mr Pompeo can expect some tough questioning at his nomination hearings. But religion is a curious and unpredictable phenomenon and the “religious” problems he encounters as secretary of state may not be the ones any of the questioners expect. During the Middle Eastern travels of Vice-President Mike Pence, a passionate evangelical, some of the greatest hostility he encountered was from fellow Christians in the region, who felt America’s recognition of Jerusalem as Israel’s capital was unhelpful to peace. He received a rave reception from Jewish members of the Knesset for a speech that was laced with scriptural references; but leaders of traditional Christian churches in the region were unwilling to meet him. Mr Pompeo should anticipate similar shocks.