Earlier this month, 18 U.S. senators wrote a letter to President Trump urging him to issue an executive order “that would require the agencies of the federal government to respect religious freedom.”

Their letter began: “The free exercise of religion — the fundamental right guaranteed to Americans to practice any faith or to choose no faith at all — is enshrined as the first freedom in the First Amendment to the United States Constitution.”

While it is unclear precisely what order the senators seek, one thing is clear: They are wrong about the First Amendment to the U.S. Constitution.

The “first freedom” is not the free exercise of religion — it is freedom from established religion.

We do not take lightly the accusation that sitting U.S. senators are incorrect regarding our Constitution. But this is not a matter of opinion; it is a matter of fact.

The First Amendment states, “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.”

This single sentence includes two important clauses each protecting different freedoms. The establishment clause protects the right of citizens to live free from government-propagated religion; the free exercise clause protects the right of citizens to observe, practice, and worship as they wish, including the right to not worship or observe anything at all.

Recognition of this complex truth does not in any way downgrade the importance of the free exercise of religion. It is a foundational right in the U.S., one that even those of no religious belief can recognize as valuable to the individual and necessary for an open and free society. But it is important to recognize — as the Founding Fathers did — that the free exercise of religion can only safely exist and flourish with a secular government.

The men who wrote the U.S. Constitution understood well that the greatest threat to freedom of conscience — of thought, belief, religion, and expression — was tyranny and, in their time, tyranny was predominantly religious in nature.

The founders were well aware of the oppression and violence that accompanied established religion in Europe. That continent had been ravaged by the brutal Thirty Years’ War, in which Protestants, Catholics and Orthodox Christians burned and killed their way across the map, leading to more than 8 million casualties between 1618 and 1648.

So when the U.S. founders had the opportunity to forge a legal framework for a new nation, they inscribed as the first freedom the right to live free from the government’s heavy hand in the area of religion.

They did this in part because they observed that government cannot change people’s minds; it can only punish them for the content of their thoughts.

As Thomas Jefferson wrote in his “Notes on the State of Virginia” in the early 1780s:

“Is uniformity attainable? Millions of innocent men, women and children, since the introduction of Christianity, have been burnt, tortured, fined, imprisoned: yet we have not advanced one inch towards uniformity. What has been the effect of coercion? To make one half the world fools, and the other half hypocrites. To support roguery and error all over the earth.”

The moment a government chooses favorites among religions, or supports religion over nonreligion, it begins down a path that leads to governmental persecution of, as well as increased societal hostilities toward, those of minority faiths and beliefs.

Without secular government, free exercise is in peril.

The Supreme Court has upheld this understanding. In Everson v. Board of Education (1947) the court ruled the establishment clause applied equally to states as well as the federal government.

Justice Hugo Black wrote broadly on the clause’s meaning:

“The ‘establishment of religion’ clause of the First Amendment means at least this: Neither a state nor the Federal Government can set up a church. Neither can pass laws, which aid one religion, aid all religions or prefer one religion over another. Neither can force nor influence a person to go to or to remain away from church against his will or force him to profess a belief or disbelief in any religion. No person can be punished for entertaining or professing religious beliefs or disbeliefs, for church attendance or non-attendance. No tax in any amount, large or small, can be levied to support any religious activities or institutions, whatever they may be called, or whatever form they may adopt to teach or practice religion. Neither a state nor the Federal Government can, openly or secretly, participate in the affairs of any religious organizations or groups and vice versa. In the words of Jefferson, the clause against establishment of religion by law was intended to erect ‘a wall of separation between Church and State.’”

While the Supreme Court has been far from consistent in its restrictions on religious involvement in government, this much has remained true: The government may not impose religious orthodoxy on individuals or society at large. Government must remain secular, and religious belief (or nonbelief) must remain a matter of personal conscience, free from government preference or encouragement.

It is true that a secular government does not by itself guarantee the protection of the free exercise of religion, but there is no doubt that absent it, religious freedom is but a pipe dream. Our constitution recognizes this truth, and ideally more of our elected officials would, too.

(Michael De Dora is the Center for Inquiry’s director of government affairs and main representative to the United Nations. Nick Little is the center’s vice president and general counsel.)