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This may cheer liberals who are worried that the White House is giving too much ground to Republicans by proposing “Chained CPI” for Social Security as part of a final fiscal cliff deal — in effect agreeing to a cut in Social Security benefits.

In an interview with me this morning, Senator Dick Durbin, a top ally of the White House, told me he opposes including Chained CPI for Social Security in the final deal. He said it would be difficult for Democrats to support Chained CPI for Social Security if it ended up in the deal, though he said it was premature to say anything definitive about how they would vote.

“We ought to deal with Social Security in a separate conversation that is not part of deficit reduction,” Durbin told me. “To do it at this stage is the wrong way to go.”

Durbin has said this before, but it’s notable that he’s repeating it in the wake of the White House’s reported offer of a deal that includes Chained CPI for Social Security.

Pressed on why the White House is backing this, given that it’s bad policy, Durbin blamed Republicans, saying they were insisting on including it in a final deal. “The president is trying to get to an agreement, and I understand that,” Durbin said. “Boehner has been adamant that he wants Chained CPI.”

“The Speaker and many of his Republican friends are hell bent on Chained CPI,” Durbin continued. “It may be part of an overall solution [later] but to do it at this stage is the wrong way to go.”

Durbin pointedly said that it would be a “hard ask” for many Senate Dems if the White House includes Chained CPI for Social Security in a final deal. But Durbin declined to rule out the possibility that Senate Democrats would ultimately support it if the White House insisted on it.

For liberals who want to prevent this from happening, their best hope may be to pressure Democratic lawmakers to declare this a nonstarter. When enough Democrats spoke out against hiking the Medicare eligibility age, the White House got the message that many in the party viewed it as unacceptable, and drew a hard line against it in the talks.