When Donald Trump spoke to a group of evangelical leaders in New York early this past summer, he insinuated that Hillary Clinton’s Christian faith was an unknown quantity, that there was really no indication in her long public life of her being religious at all. The record, of course, could hardly be clearer on Clinton’s religious affiliation; she is a lifetime Methodist who has spoken repeatedly about the formative influence of her Protestant faith. This much we have certainly learned by now: Facts rarely get in the way of Trump’s fearmongering. If it pays to suggest that Barack Obama is a secret Muslim, then surely there is something to be gained from darkly implying that Clinton might just be a closeted unbeliever. After all, the two groups that polling has consistently shown to evoke the most distrust among Americans are Muslims and atheists.

In casting doubt on Clinton’s religious credentials before an evangelical audience, Trump was simply trying to fire up those Christian soldiers who already see her as an enemy to their social and political causes. But, the insinuation itself raises the larger question of whether there remains, in effect, a religious test for the nation’s highest office, notwithstanding the constitutional provision to the contrary. Could an atheist or avowed secularist be elected to the presidency—indeed, to any office of public trust—in a country still so reflexively God-affirming?

When Richard Nixon allowed in the presidential election of 1960 that the Roman Catholic faith of his rival, John F. Kennedy, should not be an issue, he did so in such a way that offered little consolation to the nonbeliever: “There is only one way that I can visualize religion being a legitimate issue in an American political campaign,” Nixon claimed. “That would be if one of the candidates for the Presidency had no religious belief.” While Kennedy went on to become the nation’s first, and only, Catholic president, the Cold War blockade against candidates without religious belief was kept very much in place. Even now with the threat of godless communism having largely dissipated, the atheist badge remains an automatic disqualifier for more than 40 percent of the American electorate. A mere whiff of irreligion can be a serious political encumbrance, an unforgivable breach for those who still take the nation’s biblical, city-on-a-hill status with exceptional seriousness.

Raising the atheist specter against presidential candidates has been a tried-and-true part of the attack apparatus in American politics from the beginning. The sometime Anglican, mostly deist Thomas Jefferson was relentlessly assailed as a howling atheist who would destroy the biblical and Christian foundations of the republic. For many American Christians, the election of Jefferson in 1800 was apocalyptic; the political and moral order was being entrusted to an infidel indifferent to whether his compatriots worshipped one god, twenty gods, or no god at all. To Federalist clergy, if Americans elected a freethinker like Jefferson, they might as well throw their Bibles into bonfires and teach their children to chant mockeries of God.

A century-plus later in 1908 rumors followed the Republican presidential nominee, William Howard Taft, that he had “no particular religious belief.” The Taft campaign countered the whispers of atheism by trumpeting Taft’s substantial Unitarian connections, admittedly small solace to evangelicals. His Cincinnati pastor stepped forward to emphasize that Taft’s mother and father had been longtime members of the church and that their son had joined in enthusiastically as a youth, including on one occasion playing the part of a “very plump” pixie in a church play. “Taft Once Unitarian Fairy” was the headline of The New York Times story explaining how Taft met the religious bona fides for the office he was seeking. Needless to say, that report did not solve Taft’s religion problem. Evangelical opponents dogged him throughout the election season, claiming that no Christian could vote for such a heterodox candidate, especially in comparison to their champion, Presbyterian William Jennings Bryan.

Down ballot the politics of irreligion have been much the same. American unbelievers occasionally reported electoral successes, but they were usually small victories claimed under a cloud of suspicion. An atheist alderman in Lyons, Iowa—one Samuel Penn—served for years as a member of the City Council in the 1850s despite his ungodly opinions being widely known in town. His “unflinching integrity” won out over ministerial criticisms and pious misgivings. Or, then there was the freethinker who won a county election in Petaluma, California, in 1862. His opponents circulated handbills identifying him as an atheist and infidel, both names in “big capital letters,” trying to convince local Christians to vote against him, yet in his case to no avail.

Far better known than local atheist triumphs were infamous secularist debacles. One such was the fate of the convicted blasphemer Abner Kneeland who, after years of legal trouble in Massachusetts in the 1830s, set out for Salubria, Iowa, in search of freer climes. There he kept up his infidel activities, organizing celebrations of Tom Paine’s birthday and criticizing Christian “bigotry” and “superstition.” He also stayed involved in party politics. Entering the fray on behalf of the Democrats over the Whigs, he quickly became a lightning rod, with the local Democratic candidates getting tarred as “Kneelandites.” To underline the point, some hotheaded acolytes of the “Christian party in politics” burned the “Old Infidel” in effigy, a potent symbol (as they saw it) of the election’s religious and political stakes. Kneeland’s favored candidates went down in flames with his likeness.

Still more infamous was the brouhaha that erupted in 1877 over the news that President Rutherford B. Hayes was about to appoint the infidel orator and Republican politico Robert G. Ingersoll as ambassador to Germany. “Only think of committing this whole Christian Republic to the deep, deep disgrace,” one New York correspondent reported aghast, “of being represented in the German Empire by a clever, loud, contemptuous scoffer at the Christian religion and the Bible!” The nomination was quickly set aside.

The snubbing of Ingersoll lit up freethinking liberals. Here was an eminently qualified statesman, a Civil War veteran and lawyer, excluded from holding an office of public trust entirely on religious grounds. The dire message that secularists took from Ingersoll’s squashed diplomatic career and from any number of episodes like it was one of persisting disenfranchisement through Christian statecraft. As Kneeland’s old infidel newspaper, the Boston Investigator, editorialized in 1885, “Our politics this day are governed almost as much by religion as if we had a nationally established church and creed, for no man who is not religious can be elected to any office.” That despairing conclusion overstated the absoluteness of the barrier, but not by much.

Even as the number of Americans who claim no religious affiliation has grown over the last 20 years—now about 25 percent of the population—the demand that politicians make their theism manifest continues to resound. Some took the populist success of Senator Bernie Sanders, a secular Jew with thin religious ties, as an indicator that the nation’s obligatory godliness is finally tapering off. Perhaps, but a staffer at the Democratic National Committee was nonetheless caught, in a hacked email, wondering if Sanders might be an atheist and whether that could be used against him in the primaries. After he left office in 2013, Barney Frank, the first openly gay member of Congress, admitted that during his career he had never been fully candid about his nonbelief and advised atheists against using that harsh identifier in public life. Why should a politician, he asked, “pick a fight that doesn’t have to be waged?” On this front, the secularist minority still has a long way to go. Public expressions of faith, however perfunctory, retain a strong pull in America’s electoral politics. Insinuating that one’s opponent does not pass this de facto religious test has been a recurring smear in the nation’s history, one no less nefarious for its familiarity.

Leigh Eric Schmidt is the Edward C. Mallinckrodt Distinguished University Professor in the John C. Danforth Center on Religion and Politics at Washington University in St. Louis. He is the author of Village Atheists: How America’s Unbelievers Made Their Way in a Godly Nation, out in early October from Princeton University Press.