Dismissing President Obama’s embrace of Republican demands for tax breaks for billionaires and a massive estate-tax exemption for millionaires as "an absolute disaster and an insult to the vast majority of the American people," Vermont Senator Bernie Sanders has promised to "do whatever I can to see that 60 votes are not acquired to pass this piece of legislation."

The White House was trying to sell the deal Tuesday morning as a necessary bargain—meeting all the major demands of Congressional Republicans in order to achieve an extension of unemployment benefits. But Sanders was not buying that line. The senator said the Republican determination to hold jobless aid hostage to get a better deal for the rich was an "insult" and an "outrage," and he said it was "absolutely wrong" for Democrats to cut deals with them.

"Millionaires and billionaires do not need huge tax deductions. That’s the simple truth. And the fact of the matter is—despite Republican rhetoric—if we’re serious about creating jobs in this country, which should be our main priority, that’s one of the worst ways to do it.," declared Sanders. "[It’s] much better to take that money, invest in our roads, bridges, railroad systems, infrastructure. You create jobs doing that."

Pressed by MSNBC’s Ed Schultz—who referred to Obama as the "capitulator in chief"—Sanders did not rule out the prospect of a filibuster.

"I will do whatever I can on this. This is a very, very bad agreement," said Sanders, who noted polling that says the American people oppose extending tax breaks for the rich. "I think we’ve got to hold tough on this, hold firm on this and not concede to Republicans who…have absolutely no inclination to compromise. They want it all for their rich friends."

Sanders was not alone.

House Judiciary Committee chairman John Conyers, D-Michigan, said that "this is a fight for the heart and soul of the Democratic Party and the Nation. I can tell you with certainty that legislative blackmail of this kind by the Republicans will be vehemently opposed by many if not most Democrats, progressives, and some Republicans who are concerned with the country’s financial budget. I for one will do everything in my power to make certain that legislation along these lines does not pass during the lame duck session."

Vermont Congressman Peter Welch called the plan "fiscally irresponsible" and "grossly unfair." 

Welch is circulating a letter to House speaker Nancy Pelosi—which quickly attracted signatures from by a number of his fellow House Democrats—that declares: "We oppose acceding to Republican demands to extend the Bush tax cuts to millionaires and billionaires for two reasons:

"First, it is fiscally irresponsible. Adding $700 billion to our national debt, as this proposal would do, handcuffs our ability to offer a balanced plan to achieve fiscal stability without a punishing effect on our current commitments, including Social Security and Medicare.

"Second, it is grossly unfair. This proposal will hurt, not help, the majority of Americans in the middle class and those working hard to get there. Even as Republicans seek to add $700 billion to our national debt, they oppose extending unemployment benefits to workers and resist COLA increases to seniors.

"Without a doubt, the very same people who support this addition to our debt will oppose raising the debt ceiling to pay for it.

"We support extending tax cuts in full to 98 percent of American taxpayers, as the President initially proposed. He should not back down. Nor should we."

An emerging concern among congressional progressives was that, in addition to being economically unsound, Obama’s deal is politically dangerous.

Sanders summed up the sentiment, when he said: "Not only is this bad public policy—driving up the deficit, increasing the growing gap between the rich and everybody else—I think it is bad politics. It’s bad politics in the sense of: Who is going to believe this president—or anyone who votes for this—in the future when you campaigned for years against Bush’s economic policies, and then you say, ‘Oh, by the way, that’s what I’m voting for. I’m voting for tax breaks for the rich.’"