A 2011 Gallup poll reported that, for the first time, a majority of Americans said they would vote for a “well-qualified” atheist to be president. Since only 18 percent of Americans said they would support a nonbeliever in 1958, the 2011 poll represented a major step forward in the nation’s willingness to put an atheist in the White House.

As speculation about the 2016 presidential election begins to heat up, many Americans are wondering if Hillary Clinton could become the first female president of the United States. Following the election of the nation’s first African American president in 2008, this would be a powerful reminder of how old prejudices are crumbling as the country moves deeper into the twenty-first century. Given these advances, it might seem startling at first to point out that one group of Americans has no hope of seeing one of its ranks in the Oval Office in 2017: atheists.

But in spite of these gains, atheists with presidential ambitions still face serious, if not impossible, challenges. A 2014 Pew Research Center survey found that atheism remained the top negative trait for American voters. In fact, atheists continue to trail every other group polled, including gays and lesbians and Muslims. According to the Pew survey, even marijuana smokers and politicians who have had extramarital affairs are viewed more favorably than nonbelievers. Ouch.

Why does the prejudice against atheists persist when so many other groups (Catholics, African Americans, gays and lesbians, women) have gained acceptance as public office holders? Most researchers point out that the United States, unlike many European nations, remains a deeply religious country. Millions of Americans identify as evangelical Christians, whose lives revolve around their churches and their faith. And many of these Americans still seem deeply suspicious of people who don’t believe in God, viewing their lack of belief as a character flaw or an act of arrogance.

Rick Warren captured this perspective in a 2008 sermon delivered at his Saddleback Church. The popular evangelical pastor said that he could not vote for an atheist because “nobody is self-sufficient to be president by themselves. It's too big a job." Apparently dozens of presidential aides and cabinet members are no stand in for the big guy.

Not surprisingly, the tension between believers and nonbelievers is not a new one. Nearly 150 years ago, in his autobiography, British political philosopher John Stuart Mill attacked what he called the “vulgar prejudice” of those who believed that religious skepticism “is connected with any bad qualities either of mind or heart.” Religious belief, Mill argued, is no more a guarantee of goodness than the lack of that belief is a guarantee of evil. “The world would be astonished,” he concluded, “if it knew how great a proportion of its brightest ornaments—of those most distinguished even in popular estimation for wisdom and virtue—are complete skeptics in religion.”

Of whom was Mill thinking when he wrote those lines? Of George Eliot, perhaps, the great English writer and moralist, whose novels reflect her constant preoccupation with the central ethical problems of human existence. Or of the Russian writer Ivan Turgenev, whose early stories are credited with persuading Alexander II to free the serfs, and who fought his whole life for the advancement of liberty against those on the left and right who were more interested in dictatorship.

It is easy to add to this list of thoughtful, morally sensitive nonbelievers. Looking at the century following Mill’s death, one thinks immediately of such people as William James, E. M. Forster, George Orwell, Albert Camus, and Hannah Arendt—all skeptics, and yet all passionately concerned in their writing with the crucial social issues of their times and with the most difficult questions of morality.