Feinstein has endorsed Obama’s muscular counterterrorism policy, at some cost to her reputation among civil libertarians. Lately, she has also been criticized for defending the legality of the National Security Agency surveillance exposed by Edward Snowden. Her critics may detect a reputation-reviving opportunism in her recent dudgeon toward the C.I.A. But it was under Feinstein, after 2009, that the Select Committee took on an ambitious investigation into the defunct black sites. Senate investigators worked in a skiff near C.I.A. headquarters, in Virginia. Under a protocol that Feinstein described last week, the agency provided a segregated computer network and loaded in some six million pages of classified documents. Several times, by Feinstein’s account, C.I.A. officers secretly withdrew documents from the Senate staff’s collection. When they were caught, she said, they claimed, falsely, that the White House had ordered their action. The agency later apologized.

One of the questions that the committee explored was whether torture worked—that is, whether it produced exclusive intelligence that saved innocent lives. Even if it did, it would be wrong as policy, because it is immoral; but during the investigation former C.I.A. leaders said that the interrogations had proved very valuable and would withstand history’s judgment. Many Americans still think that such claims might be true, but they have no way to evaluate them, since the facts on which they are purportedly based remain highly classified.