RS Commissioner John Koskinen has declined to testify in his own defense at a congressional hearing Tuesday, but insisted in a statement that his bungling of a subpoena doesn’t rise to the level of “treason, or high crimes and misdemeanors” needed for him to be impeached. The Judiciary Committee hearing is being viewed by some House Republicans as the precursor to impeachment, with the House’s top investigator saying Mr. Koskinen defied a congressional subpoena that demanded all of former IRS senior executive Lois G. Lerner’s emails be preserved as part of the investigation into tea party targeting. But Mr. Koskinen,...