Defense Secretary Ash Carter has sent a 23-page "heartburn" letter to Capitol Hill threatening to support a presidential veto of the fiscal year 2017 defense authorization bill. The July 13 letter , obtained by Inside Defense , comes as House and Senate lawmakers prepare to enter conference committee negotiations on their respective bills, which are $18 billion apart and seek a variety of different reforms to the Pentagon's acquisition system and management structure. "My first and most urgent concern is...