The tit-for-tat over avoiding the fiscal cliff slogged onward Sunday, as Senate leaders remained essentially stuck following a frantic day of horse-trading and bitter attacks by both Democrats and Republicans. 
 
 (PHOTOS: 11 side effects of going over the cliff) 
 
 Both sides now have 48 hours to resolve their differences, or risk a double whammy of historic tax hikes and spending cuts that will make them even more unpopular outside-the-Beltway. 
 
 After every breakthrough, there seemed to be a new obstacle standing in the way of a deal, underlining the perception that the nation’s lawmakers and the White House simply can’t come to terms with each other. Vice President Joe Biden — who had remained on the sidelines for much of the negotiations — returned to Washington on Sunday after Senate Minority Leader Mitch McConnell (R-Ky.) requested it. 
 
 “Mr. President, I rise today frustrated, embarrassed and angry,” said West Virginia Democratic Sen. Joe Manchin on the floor Sunday. “It is absolutely inexcusable that all of us find ourselves in this place at this time, standing on the floor of the Senate in front of the American people hours before we plunge off the fiscal cliff. With no plan and no apparent hope.” 
 
 After loud Democratic protests on Sunday, Republicans agreed to take off the table a controversial provision that would have cut Social Security benefits. But more hurdles emerged, including over automatic spending cuts set to take place next year, and the rates for estate taxes that are set to balloon if no deal is reached by the new year. 
 
 (PHOTOS: Fiscal cliff's key players) 
 
 With no deal at hand, Senate leaders were preparing alternative plans to avoid the cliff’s full impact, including a fall-back option floated by Democrats to force through an extension of current tax rates for families who make less than $250,000, as well as new spending measures to extend jobless benefits for two million unemployed Americans. Republicans were still weighing whether they’d demand 60 votes for passage of even a limited measure, though the prospects for such a bill in the GOP-controlled House remained bleak. 
 
 The House Republican leadership moved Sunday night to give itself expedited authority to bring legislation to the floor in case there was an opening. 
 
 There is also clearly growing tensions between McConnell and Senate Majority Leader Harry Reid (D-Nev.), the pair who took over the fiscal cliff talks on Friday following weeks of fruitless discussions between President Barack Obama and Speaker John Boehner (R-Ohio). 
 
 Democrats are angry at McConnell, believing he’s adopted the “majority of majority” standard Boehner has demanded in the House for the Senate. McConnell does not believe Reid is playing straight with him, saying the Nevada Democrats has shown little urgency by dragging his feet through the weekend of talks. 
 
 McConnell even called in Biden to help break the logjam, although the vice president has offered nothing different from Reid’s position. 
 
 “There is still significant distance between the two sides, but negotiations continue,” Reid said Sunday evening, announcing that the chamber would return to session Monday morning. 
 
 On Sunday afternoon, a new sticking point emerged over “turning off” the sequester, the tens of billions of dollars in spending cuts slated to hit the Pentagon and federal agencies beginning Jan. 2. Democrats want to use some of the revenue from the increased taxes of a cliff deal to postpone those cuts. Republicans, however, are objecting to that proposal, saying they want savings from other areas. 
 
 Democrats have floated a potential compromise to use a portion of the new revenue and other savings from a cliff deal — a “50/50 split” — to “turn off” the sequester, but it is unclear if GOP leaders will agree to that offer. 
 
 And Biden’s inclusion in the negotiations — similar to the role he played in previous legislative fights involving McConnell, an old Senate colleague — sets up a “good cop, bad cop” scenario for Democrats, with Reid playing the heavy and Biden able to work more closely with GOP leaders on Capitol Hill. ||||| “Talk to Joe Biden and McConnell,” Mr. Reid told reporters when asked if negotiations were continuing. 
 
 In the balance are more than a half-trillion dollars in tax increases on virtually every working American and across-the-board spending cuts that are scheduled to begin Tuesday. Taken together, they threaten to push the economy back into recession. 
 
 “It looks awful,” said Senator Richard J. Durbin of Illinois , the second-ranking Democrat. “I’m sure the American people are saying, with so much at stake why are they waiting so late to get this done?” 
 
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 Senator Lindsey Graham , Republican of South Carolina , who had said early Sunday that he thought a deal was within reach, said later on his Twitter feed, “I think we’re going over the cliff.” 
 
 Weeks of negotiations between President Obama and Speaker John A. Boehner inched toward a deal to avert the so-called fiscal cliff, while locking in trillions of dollars in deficit reduction over 10 years and starting an effort to overhaul the tax code and entitlement programs like Medicare . But earlier this month, Mr. Boehner walked away from those talks. 
 
 Instead he tried to reach a much more modest deal to avoid a fiscal crisis by extending the expiring tax cuts for incomes under $1 million. When Mr. Boehner’s own Republican members revolted, he ceded negotiations to the Senate. But compromise has proved equally elusive in that chamber. 
 
 Absent a last-minute deal, Mr. Reid is expected to move on Monday to bring to a vote a stopgap measure pushed by Mr. Obama, which would retain lower tax rates for incomes below $250,000 and extend unemployment benefits. But it was not clear that would even get a vote. The objection of a single senator on Monday would run out the clock on the 112th Congress before a final tally could be taken. 
 
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 Mr. Obama appeared on the NBC program “Meet the Press” on Sunday and implored Congress to act. “We have been talking to the Republicans ever since the election was over,” Mr. Obama said in the interview. “They have had trouble saying yes to a number of repeated offers.” 
 
 He added, “Now the pressure’s on Congress to produce.” 
 
 After the talks broke down over the inflation demand, Senate Republicans emerged from a closed-door meeting on Sunday afternoon to declare the issue off the table for now. Senator John McCain , Republican of Arizona , said that holding the line against raising taxes on high-income households while fighting for cuts to Social Security was “not a winning hand.” 
 
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 Then they mustered a new talking point, saying Democrats want to raise taxes only to spend more money. Their new objection: Democrats are seeking a one- to two-year “pause” for across-the-board spending cuts and an extension of expired unemployment benefits for two million people. 
 
 “We raise taxes, and we spend more?” asked Senator Kay Bailey Hutchison , Republican of Texas . “It’s business as usual.” 
 
 For their part, Democrats beat back the inflation proposal, and then promptly proclaimed themselves incensed that Republicans would not soften their position on a generous level of taxation on inherited estates and an insistence that a final deal permanently prevent the alternative minimum tax , a parallel tax system meant to ensure that wealthy people pay more, from expanding to affect more of the middle class. 
 
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 Democrats were also demanding that across-the-board cuts to military and domestic programs — known as the “sequester” — at least be delayed. 
 
 “We’re not here to defend government, we’re here to make sure of the defense of our country,” said Senator Barbara A. Mikulski , Democrat of Maryland , whose state would be hit particularly hard. “Sequester has consequences.” 
 
 Senate Democratic aides were openly making legislative plans for later this week, to press Democratic proposals after the fiscal deadline is breached — and after the next Congress is sworn in on Thursday with more Democrats in both the House and the Senate. 
 
 But officials close to the negotiations said the talks were continuing, centered for now on a new axis, Mr. McConnell and Mr. Biden. 
 
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 Much of the umbrage was oddly discordant. Mr. Obama has long advocated for a permanent fix to the alternative minimum tax, which must be “patched” each year to keep it from applying to middle-income families. Until this weekend, both Democrats and Republicans appeared willing to let the across-the-board cuts take effect, at least temporarily, while a larger deficit deal is negotiated early next year. 
 
 Indeed, many Republicans were the loudest in protesting the cuts. Now that Democrats want them canceled, Republicans equate that position to raising taxes in order to spend more. 
 
 On some of the biggest sticking points, the two sides are now inches apart. Barely a week after House Republicans refused to vote to allow taxes to rise on incomes over $1 million, Senate Republicans proposed allowing tax rates to rise on incomes over $450,000 for individuals and $550,000 for couples. Democrats countered with a proposal to extend expiring Bush-era tax cuts up to $360,000 for individuals and $450,000 for couples. For both sides, that meant major movement. Mr. Obama has been holding firm at a $250,000 threshold. 
 
 Of course, a big question hung over the negotiations in the Senate: even if the Senate can find an accord, would it pass the House? 
 
 Even on the estate tax , the two sides are not far apart, although their language is. Republicans want to tax estates valued above $5 million at 35 percent. Democrats want to tax inheritances above $3.5 million at 45 percent. 
 
 If that sounds like a bridgeable divide, Democrats are not conceding an inch. “The net result is that 6,000 Americans would get a $1-million-a-year tax break on their estate tax,” Mr. Durbin said. “The Republicans once again are ready to shut us down over not 2 percent of the population, but 0.1 percent of the population.”
– With the fiscal cliff in sight, Democrats and Republicans are no longer talking. Senate Majority Leader Harry Reid and Minority Leader Mitch McConnell reached a "major setback" today over a fairly wonky provision known as "chained CPI," Democratic sources tell Politico. A means of calculating entitlement benefits, CPI is anathema to many liberals because it would give Social Security beneficiaries lower payments. And Democrats say they have made other concessions, like raising taxes only for those earning more than $400,000. McConnell spoke on the Senate floor today, saying Republicans hadn't received a response to their offer from last night, the New York Times reports. Reid responded that Democrats had no counter-offer because they were "apart on some pretty big issues." President Obama said today on Meet the Press that he would accept "chained CPI" but only as part of a bigger deal that includes at least $1.2 trillion in new revenue over a decade. As it stands, Reid and McConnell are cutting a smaller deal to head off certain tax hikes and Medicare cuts, without tackling the deficit or preventing $109 billion in defense and domestic spending cuts slated for this year.