General James Wilkinson sent a letter about Aaron Burr to President Thomas Jefferson on Oct. 21, 1806. Accused of treason, Burr asked the trial judge — Chief Justice John Marshall — to issue a subpoena duces tecum commanding President Jefferson to hand over copies of some military orders concerning Burr and the original Wilkinson correspondence, in his own handwriting, for use in cross examining the general. “The letter from Wilkinson — who turned out to be a paid agent of Spain — in fact triggered Jefferson’s decision to …