Washington seems to be barreling toward a constitutional crisis. Democrats are barraging President Trump with demands for witnesses and documents. Trump has answered by stonewalling, vowing to fight “all the subpoenas.” As House Speaker Nancy Pelosi warned, Trump seems to be goading the Democratic-controlled House toward impeachment, perhaps because it’s a battle he thinks he can win. Politicians on both sides are repairing to their tribal corners. Is there anyone who can serve as honest referees in this partisan standoff? One answer — don’t laugh — is lawyers. Specifically, Republican lawyers. Even as Republicans in Congress have fallen in line...