In the middle of the first presidential impeachment trial, of Andrew Johnson in 1868, Walt Whitman wandered over to Capitol Hill to witness the proceedings. “Our American politics,” the poet told a friend, “are in an unusually effervescent condition.”

A century and a half later — and 127 years after Whitman’s death — our American politics are in an unusually effervescent condition again. In a month that included President Donald J. Trump’s State of the Union address, it became increasingly clear that there were several moving parts to American politics — and that American politics was changing dramatically, and importantly.