“He,” a somber Rabbi Isaac Mayer Wise intoned after the assassination of Abraham Lincoln, “is a sin-offering for our iniquities.” This sentiment, expressed in a black-draped congregation in Cincinnati, was echoed in countless other memorial services across the North. Peace had been declared but days before; now, synagogues recited the Kaddish for the fallen president.

In New York City, Shearith Israel broke with custom by chanting a Sephardic mourning prayer it had never before said for a gentile. Jews were in the midst of celebrating Passover; now Lincoln, like Moses, had succumbed at the threshold of the Promised Land. In Cincinnati, Wise ended his sermon with words that may have stunned his hushed audience (we have no record of the response)....