Don't let America's big idea dissolve into something else

I love being at the Smithsonian's National Portrait Gallery in Washington, D.C. Among other exhibits, it houses America's official presidential portraits, which I find so compelling I visit and revisit them. I'm especially intrigued by the unfinished Gilbert Stuart portrait of George Washington and the life-size portrait of Abraham Lincoln.

I am profoundly grateful to these two men and to those who along with them founded a nation on the improbable idea that a diverse people can live free and self-govern. Originally meant only for landed white men, historian Jane Kamensky called our founding idea "leaky" in the PBS Ken Burns series "The American Revolution."...