Spencer W. McBride is a historian and author of "Pulpit and Nation: Clergymen and the Politics of Revolutionary America."

In an unprecedented move, the Rev. Patrick J. Conroy resigned as chaplain of the House of Representatives amid his two-year term. The resignation came at the behest of House Speaker Paul D. Ryan.

It appears that Ryan’s move was motivated in part by politics — namely a moment before debates over tax reform, in which Conroy prayed that lawmakers could find a compromise that would “guarantee that there are not winners and losers under new tax laws, but benefits balanced and shared by all Americans.” The prayer reportedly irked several conservative congressmen.

Though Ryan (R-Wis.) denied it, the possibility that partisan motives drove his action has prompted a predictably partisan response. Some members of Congress have called for an investigation, and House Minority Leader Nancy Pelosi (D-Calif.) called the move “impossible to support.”

This dispute was perhaps inevitable. Although the House chaplain (and the Senate chaplain, for that matter) have largely remained invisible and noncontroversial throughout American history, the rest of the nation’s clergy have often plunged into political debates, prompting outcries from the opposition that they should stick to saving souls. It makes sense that, in this especially polarized era, this tendency to pounce on the perceived politics of the clergy would spill over into Congress.

There is, however, a historical irony in a chaplain’s sudden appearance at the center of controversy among members of Congress. This is because the very first American congressional chaplain, Jacob Duché, was appointed primarily to promote civil discourse on the legislative floor.

In 1774, the newly formed Continental Congress met in Carpenters’ Hall in Philadelphia. Things got off to a rocky start. The delegates were almost instantly embroiled in an argument over whether each colony would get an equal vote in debates or votes would be determined by a colony’s population and “importance.” As John Adams tells it, the fraught nature of this debate prompted Thomas Cushing of Massachusetts to motion that Congress “should be opened with prayer.”

Even this suggestion proved to be a source of controversy because the delegates belonged to an array of Christian denominations and could not agree on the religious affiliation of the clergymen they invited to pray. Furthermore, selecting a chaplain from one denomination at the exclusion of the others might appear like preferential treatment and alienate some of the colonists the delegates hoped would support their resistance to British imperial policies. As such, John Jay of New York objected to the motion.

Samuel Adams then arose to assert that he was “no bigot, and could hear a prayer from a gentleman of piety and virtue, who was at the same time a friend to his country.” Adams suggested that Duché, the rector of Philadelphia’s Christ Church, was such a man. So Duché was invited to open the session on the following day with prayer. Duché’s prayer was so well received by the delegates that he was invited to serve as the Congress’s regular chaplain.

Duché’s appointment set a precedent. The chief criterion for congressional chaplains from that time forward was that the selected clergyman be a person of “piety and virtue, who was at the same time a friend of his country.”

Denominational diversity was an important consideration for the Continental Congress. Following Duché’s resignation in October 1776, Congress appointed two chaplains of different denominations, largely to demonstrate to citizens that the new legislative body would not favor one religious group over another.

In terms of promoting civil discourse, the move seemed to work. Several days after Duché began praying in Congress, Joseph Reed, a delegate from Pennsylvania, called the appointment of a chaplain a “masterly stroke of policy” with a “good effect.”

Years later during a particularly heated moment at the Constitutional Convention of 1787, Benjamin Franklin invoked the precedent of congressional prayer to suggest it as a means of restoring civility to the convention floor. His motion was rejected, but the fact that he made it demonstrates that he believed the inclusion of chaplains and prayer could affect the way government leaders with differing opinions engaged with each other.

In the years following ratification of the Constitution, congressional chaplains continued to offer prayers on the legislative floor. Indeed, it has endured as a nonpartisan tradition. The position and the ritual have become so routinized that the chaplains — and the prayers that they speak — rarely receive any public attention. The extent to which chaplains continued to calm heated moments in Congress is almost impossible to measure, but lawmakers have come to expect their presence and prayers at the start of each day’s work.

At times, members of Congress have voiced interest in making sure that the men who hold the chaplaincy reflect a broad range of American religious affiliations. Notably, in 1999, a group of Catholic congressmen successfully challenged the proposed appointment of a protestant chaplain, demanding the appointment of the first Catholic chaplain. Even this push, however, was about denominational representation, not political views.

But this deep congressional tradition cannot withstand the pressure from the growing polarization of American politics. And perhaps we should not be surprised.

While the congressional chaplain has avoided controversy in the past, the clergy in American politics has not. From the revolutionary era onward, preachers have used their respective pulpits to speak out on the most sensitive political issues of the day — slavery, civil rights, abortion. Americans across the political spectrum have been exceptionally tolerant of such mixing of the sacred and the secular so long as the clergyman speaking up agrees with their own views. But when factions or parties discover that a clergyman opposes their politics, the knee-jerk reaction is to declare that such clergymen have become “too political” and should stick to the Kingdom of God, leaving the government of men to elected officials.

Every week in churches throughout the country, clergymen offer sermons and prayers that urge men and women to pay special attention to the needs of the poor and those whom society has marginalized. Conroy did not pray for anything radical, offensive or even particularly political; this principle is at the heart of all religions.

Yet when the same, seemingly noncontroversial sentiment is uttered in a polarized chamber of Congress, sensitive political agendas will too often serve as the lens through which lawmakers view such remarks. At stake in the firing and replacing of Conroy as chaplain is the transformation of a congressional position designed to promote civil discourse into nothing more than another tool of partisanship.