As Democrats push forward with a plan to haul Attorney General William Barr before a federal judge for contempt of Congress, a stunning admission by House Judiciary Committee Chairman Jerrold Nadler could torpedo that case, legal experts say. The House Judiciary Committee last week took the first step toward holding Mr. Barr in contempt for defying a Congressional subpoena demanding special counsel Robert Mueller’s “full unredacted” report along with all the supporting evidence. Republicans say he even rejected an amendment that sought to carve grand jury information out of the subpoena, issued in March. But Mr. Nadler now says he...