Two words, according to Jane Mayer's must-read: Rahm Emanuel:
Emanuel adamantly opposed a number of Holder’s decisions, including one that widened the scope of a special counsel who had begun investigating the C.I.A.’s interrogation program. Bush had appointed the special counsel, John Durham, to assess whether the C.I.A. had obstructed justice when it destroyed videotapes documenting waterboarding sessions.
Holder authorized Durham to determine whether the agency’s abuse of detainees had itself violated laws. Emanuel worried that such investigations would alienate the intelligence community. But Holder, who had studied law at Columbia with Telford Taylor, the chief American prosecutor in the Nuremberg trials, was profoundly upset after seeing classified documents explicitly describing C.I.A. prisoner abuse. The United Nations Convention Against Torture requires the U.S. to investigate credible torture allegations. Holder felt that, as the top law-enforcement officer in the U.S., he had to do something.
Emanuel couldn’t complain directly to Holder without violating strictures against political interference in prosecutorial decisions. But he conveyed his unhappiness to Holder indirectly, two sources said. Emanuel demanded, “Didn’t he get the memo that we’re not re-litigating the past?”
I wonder if Emanuel was also quietly behind the decision not to reinvestigate the Gitmo "suicides".