When W.F.K. Travers’s 9-foot-tall painting of Abraham Lincoln was first unveiled to America at the 1876 Centennial Exhibition in Philadelphia, Pennsylvania, it stood alongside Gilbert Stuart’s “Lansdowne Portrait” of George Washington—and together, the likenesses of America’s two most esteemed presidents stunned viewers. The oil-on-canvas portrait of Lincoln was painted from life in 1865, mere months…