In the long and contested history of law wielded as political instrument, the abrupt resignation of Joe diGenova from the Justice Department marks another moment where the machinery of prosecution and the imperatives of power appear to strain against one another. Appointed just five months ago to lead a sweeping inquiry into alleged conspiracies by Obama- and Biden-era officials, diGenova departed Thursday without explanation, even as grand jury subpoenas were beginning to reach witnesses. His exit follows the earlier removal of a predecessor who questioned the evidence, and it leaves two majo