Abraham Lincoln’s assassination on April 14, 1865, confronted the American public with urgent political challenges that would shape the trajectory of the post-Civil War United States. But a religious controversy that erupted during the subsequent weeks of national mourning would raise enduring social and moral questions about what it means to be both deeply patriotic and religiously observant in America.Shortly after Lincoln’s murder, President Andrew Johnson declared a “day of humiliation and mourning,” upon which he recommended that his fellow citizens across the country gather in their respective places of worship to lament the late president’s tragic demise. But in doing so, Johnson had unwittingly created a significant dilemma for American Jews. His chosen date—June 1, 1865—happened to coincide with the Jewish holiday of Shavuot, which commemorates God’s revelation of the Law at Mount Sinai.Today, the holiday is popularly observed among Orthodox and various traditionalist Jews but largely ignored by others. In an article for the American Israelite newspaper, leading 19th-century Reform Rabbi Isaac Mayer Wise described a similar state of affairs in mid-19th-century America. (Later in the century, American Reform communities increasingly began to celebrate Shavuot as a confirmation day.) But traditionalist Jewish congregations, including some of the most prominent synagogues in the nation, had long observed Shavuot by reading customary mystical and liturgical Jewish texts, many still recited today, that reinforced fealty to the Torah’s commandments—and these congregations often saw large crowds on Shavuot, even inviting non-Jewish dignitaries to attend. So while not all American Jews observed Shavuot at the time of Lincoln’s assassination, those who did considered it one of Judaism’s happiest occasions, upon which Jewish law prohibits any expressions of mourning.Many American Jews in 1865, therefore, faced what seemed like a stark choice between duty to country and duty to God—between patriotism and piety. As Shavuot drew near, Jewish writers, political activists, and spiritual leaders throughout the United States began in earnest to weigh in on the matter. Out of their respective solutions emerged two different models for how faith communities should serve the public square: compliance and conviction.The compliance model was best exemplified by Rabbi Sabato Morais, the leader of Philadelphia’s oldest synagogue, Mikveh Israel. In a sermon delivered over Shavuot in 1865, Morais firmly urged his co-religionists to observe the national day of mourning and humiliation without reservation. “Hebrews of America,” Morais thundered, “repress the joyful emotions that thrill your hearts!” Although he maintained that Jews must maintain “unswerving fidelity to the Law of Sinai,” he could not justify fully expressing the happiness that Jewish law demanded on Shavuot. “Great is our joy this day,” Morais conceded, “yet, incomplete, by reason of the dear object so suddenly borne away from our earthly vision.” In this view, religious communities could best serve the public square by complying with the broader, American civic spirit. In order to forge a single, righteous collective, the country’s diverse multitudes should feel responsible to transform themselves for the better.In diametric opposition stood the conviction model embodied by Jacques Judah Lyons, the rabbi of New York’s legendary Congregation Shearith Israel. Like Morais, Lyons was an ardent patriot who profoundly admired Lincoln. But in contradistinction to his Philadelphian colleague, Lyons insisted that his congregation could not observe a day of mourning and humiliation. In remarks offered on that very day, Lyons argued: “The rules of our ritual prohibit every demonstration of sorrow and all supplicatory invocation on this day of joy. But for this restriction we too, in common with our fellow-citizens of all denominations, would have observed this day of humiliation.”Lyons was determined, however, to commemorate Lincoln’s memory in an authentically Jewish manner. As he noted, the widespread practice on major Jewish holidays like Shavuot was to recite a prayer requesting happiness for the souls of departed members of the community. “In this spirit,” Lyons explained, “believing that the merits of our departed President will find favor with an all-merciful God, let us pray for the reception of his soul into the kingdom of Heaven.” For Lyons, the American public would not be well served by its Jewish constituents compromising their faith in the name of social cohesion. Instead, the greatest gift that faith communities could give to the public square is to maintain the courage of their convictions and so bequeath their unique traditions of wisdom to America as a whole.It is unclear whether either model decisively carried the day for American Jews on Shavuot in 1865. But in a broader sense, the pressures of modern American life in the 19th century certainly militated in favor of compliance, much as they do today. Recently, however, the conviction model has gained increasing cultural potency, whether in the careers of Jewish politicians like former Sen. Joseph Lieberman, in the writings of Jewish intellectuals like New York Times columnist and editor Bari Weiss, or in the increasingly widespread popularization of the Daf Yomi—daily Talmud study—among Jews of all denominational and post-denominational stripes. Where American Jewry goes from here is anyone’s guess, but much as in 1865, the answer may hold the key to interpreting not only the Jewish present, but the Jewish future.