Despite Mitch McConnell asking Vice President Biden to intervene, the two sides have failed to reach a deal so far.

With fiscal cliff negotiations stalled, Senate Republican Leader Mitch McConnell has called his old dance partner Vice President Joe Biden in from the sidelines.

"I have also placed a call to the vice president to see if he could help jump start the negotiations on his side," McConnell said on the floor Sunday afternoon. "The vice president and I have worked together on solutions before and I believe we can again."

Biden steps in as talks between Reid and McConnell stalled overnight over Republicans' insistence that a deal include changes to how the government calculates entitlement benefits, a reform known as "chained CPI."

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Democrats have rejected the proposal, arguing that their willingness to discuss chained CPI was only in the context of a grand bargain that included entitlement and tax reform, not the scaled-back package Senate leaders are now attempting to craft.

Chained CPI calculations would reduce the benefits Medicare, Medicaid and Social Security beneficiaries would receive, a reform many Democrats oppose. On the Senate floor Sunday afternoon, Reid reiterated that opposition saying "we're not going to have any Social Security cuts."

And, in a move that has mystified Republicans, Reid added that "at this stage, we're not able to make a counteroffer."

Republicans don't understand why Reid won't keep the negotiations moving by making a formal counteroffer that doesn't include chained CPI. McConnell said Republicans made their last offer at 7 p.m. Saturday night and have not heard back from Democrats since. After a meeting of Republican senators Sunday afternoon, Sens. Olympia Snowe, Bob Corker and Dean Heller all said the GOP had taken the proposal off the table.

Reid emerged from a meeting of his Democratic colleagues and said the GOP was right to take chained CPI off the table, but told reporters, "We're still left with a proposal they've given us that protects the wealthy and not the middle class."

Reid said he made a counteroffer, but did not discuss the details. A Reid spokesman walked back the majority leader's statement, saying he has not made a counteroffer. "I'm concerned about the lack of urgency here," McConnell said.

Republican aides would not say what was in their most recent offer. But privately some suggest that Reid may have been stalling for time until he could address his colleagues during a closed door meeting this afternoon.

A Senate Democratic leadership aide called the GOP's decision to inject chained CPI into the talks last night "a major setback."

But in his remarks on the floor, Reid still held out hope for a deal saying, "I'm not overly optimistic but I am cautiously optimistic that we can get something done."