Consider it a twist on the old question about a tree falling in the forest with no one to hear it: If the House adopts articles of impeachment but never sends them to the Senate, is a president truly impeached? A Harvard law professor, who also served as a Democrat-called impeachment witness, answered with a resounding “no” in a column that speaks to the deep dilemma House Speaker Nancy Pelosi faces as she sits on two articles of impeachment against President Trump. Pelosi, D-Calif., is apparently using the delay as leverage to extract favorable terms for a Senate trial. But...