Progressive members from safe blue districts, egged on by celebrities, pundits, and academic coastal elites are ratcheting up the pressure to impeach President Trump. House Speaker Nancy Pelosi may cave to their demands but not because she is threatened with being ousted. The naive liberals in her caucus may have visions of pushing Pelosi even further to the left, especially on impeachment, but the speaker knows they can’t get rid of her. Unlike former Republican House Speaker John Boehner, who resigned the speakership under pressure from his right flank, Pelosi has no such worries. She saw what happened to Boehner...