It’s as if nothing happened. Special counsel Robert Mueller and the Justice Department found no wrongdoing by President Trump, so House Democrats stepped up their calls for impeachment. Judiciary Committee Chairman Jerry Nadler issued a subpoena for millions of pages of evidence gathered by Mr. Mueller, including grand-jury material, which is secret under the law. When the department didn’t comply, Democrats said there was a “constitutional crisis,” and the committee voted to hold Attorney General William Barr in contempt. Yet if there is a constitutional crisis, its source is the Democrats. They are abusing the powers of investigation and impeachment...