Could there be a more ironic backdrop to the debate over Republican presidential candidate Ben Carson's comments about Islam and the presidency?
It rages as Pope Francis prepares to speak this week to the U.S. Congress, in a nation where Catholics were once banned from holding public office for fear their allegiance would be to Rome.
Asked Sunday on NBC's "Meet the Press" whether a president's faith should matter, Carson said, "I guess it depends on what that faith is. If it's inconsistent with the values and principles of America, then of course it should matter."
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Then Carson added, "I would not advocate that we put a Muslim in charge of this nation. I absolutely would not agree with that."
Carson was, of course, expressing his personal view and did not call for barring Muslims from the presidency. But many constitutional scholars say Carson's view is at odds with the design of the nation's founders.
Such a sentiment would very likely have surprised Thomas Jefferson, who wrote in 1821 that Virginia's religious freedom law was meant to apply to "the Jew and the Gentile, the Christian and the Mahometan," a term then used to mean Muslim, "the Hindoo and infidel of every denomination."
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Says Akhil Reed Amar, a constitutional expert at Yale, "One of the most striking features of the Constitution is how it goes out of its way to insist that the federal government is open persons of all faiths or no faith in particular."
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Article VI requires public officials to be "bound by oath, or affirmation, to support this Constitution." Then it adds, "But no religious test shall ever be required as a qualification to any office or public trust under the United States."
At the time of the founding, a dozen states imposed religious qualifications for holding office, and some explicitly barred non-Protestants. New York required an oath disavowing allegiance to a foreign prince, meaning the Pope, to disqualify Catholics.
The Constitution doesn't define the term "religious test," and the Supreme Court has never ruled directly on what Article VI means, though it has referred to the provision as banning "religious oath tests."
Oliver Ellsworth, a delegate to the Constitutional Convention who became the Supreme Court's third Chief Justice, wrote in 1787 that a religious test "is an act to be done, or a profession to be made ... for the purpose of determining whether his religious opinions are such, that he is admissible to a public office."
John Kennedy, the first Catholic US president, referred to the provision during his 1960 campaign, saying advocates of a religious test "would work to subvert Article VI."
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"If this election is decided on the basis that 40 million Americans lost their chance of being president on the day they were baptized, then it is the whole nation that will be the loser," he said.
While Article VI is seen as banning only religious oaths, the First Amendment's guarantee of religious freedom goes much further.
In 1961, the US Supreme Court struck down any kind of religious standard for public office — even a requirement to profess a belief in God. In acted in the case of Roy Torcaso, who sought appointment as a notary public in Maryland.
The state constitution required "a declaration of belief in the existence of God" to hold "any office of profit or trust." Because he was an atheist, Torcaso refused to make such a statement, and his appointment was revoked.
In ruling for him, the justices said "we repeat and again reaffirm that neither a state nor the federal government can constitutionally force a person to profess a belief or disbelief in any religion." The court ruled unanimously, relying on the First Amendment's guarantee of religious freedom.
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Taken together, says Yale scholar Akhil Amar, these constitutional provisions were "absolutely revolutionary. This is one of the biggest ideas in the Constitution, that we're going to have a system open to all."
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Beyond the legalisms, Amar says the country has thoroughly absorbed the principle. "In a nation founded by Protestants, the current US Supreme Court consists of six Catholics and three Jews, and two of the four men on Mt. Rushmore — Thomas Jefferson and Abraham Lincoln — were not regular churchgoers."
And he notes that in the last presidential election, of the four candidates for president and vice-president, only one was a protestant — Barack Obama. Joe Biden and Paul Ryan are Catholics, and Mitt Romney is a Mormon.