WASHINGTON—It was a text-message debate that led Scott Sandage and Jonathan White to discover a vital American artifact last weekend: a long-forgotten letter showing how Frederick Douglass really felt about a statue of Abraham Lincoln and a slave.
Messrs. Sandage and White are history professors who have been on opposite sides of a dispute over the Emancipation Memorial near the U.S. Capitol, which depicts Lincoln in the act of freeing a kneeling Black man.
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