"I completely agree with Senator Feinstein that this is a matter of great seriousness," she told reporters on Thursday. "You take on the intelligence community, you're a person of courage. And she does not do that lightly."
It's "pretty appalling what is being alleged or charged," she said.
She said she hadn't seen many statements from CIA Director John Brennan about the allegations, "but what I have seen are befuddling."
Senate Majority Leader Harry Reid (D-NV) also stood by Feinstein. House Speaker John Boehner (R-OH) and Senate Majority Leader Mitch McConnell (R-KY) said they wouldn't comment while an investigation was ongoing.