There are a lot of complicated ways in which to describe the schemes being floated by President Obama and congressional Republicans to abandon the traditional Consumer Price Index in favor of the so-called “chained-CPI” scheme. But there is nothing complicated about the reality that changing the calculations on which cost-of-living increases for Social Security recipients are based has the potential to dramatically reduce the buying power of Americans who rely on this successful and stable federal program.

So the word for what is being proposed is “cut”—as in: President Obama and congressional Republicans are proposing to cut Social Security.

“This is a cut affecting every single beneficiary—widows, orphans, people with disabilities and many others. It is a cut which hurts the most those who are most vulnerable: the oldest of the old, those disabled at the youngest ages, and the poorest of the poor. Perhaps fittingly, this will be done during the holiday season, when the American people are distracted,” says Nancy Altman, the founding co-director of the advocacy group Social Security Works. “They will cut Social Security not openly but by stealth—through a cruel cut known colloquially as the chained CPI.”

This is what Democrats—and most Republicans—said during the recently finished campaign that they would never do.

If Obama cuts the deal, he will, in the words of CREDO political director Becky Bond, be engaging in a “massive betrayal” of his own campaign commitments, and of the voters who reelected him barely a month ago.

The question is whether the president’s backers will back the betrayal.

The only responsible response is to say “No!”

The American Association of Retired People has does just that, rejecting the “chained-CPI” scheme as a “dramatic benefit cut would push thousands more into poverty and result in increased economic hardship for those trying desperately to keep up with rising prices.”

In this case, AARP speaks not just for seniors but for the vast majority of voters. Sixty percent of voters say it is unacceptable to change the way Social Security benefits are calculated so that benefits increase with inflation at a slower rate than they do now, according to a new Washington Post/ABC News poll.

Needless to say, those numbers put congressional Democrats and progressive interest groups in a bind. They can look the other way as President Obama cuts a deal that cuts Social Security, or they can do what the American people expect them to do: raise their voices in loud objection—so loud that the president has no choice except to keep his campaign promises. For congressional Democrats, the stakes are much higher than they are for Obama. The president is done with elections. But the Democratic Party must compete in elections to come, and the fight that is now playing out will define whether they do so as defenders of Social Security or as a party that is always on the watch for ways to compromise with House Budget Committee chairman Paul Ryan and other Republicans who salivate at the prospect of weakening and eventually privatizing Social Security.

No one will be surprised that Senator Bernie Sanders, the Vermont Independent who has been a stalwart defender of Social Security, Medicare and Medicaid is objecting.

“I want him to keep that promise,” Sanders says of the president’s commitment on the campaign trail and in the early stages of the fiscal-cliff negotiations to keep Social Security “off the table.” Adds Sanders: “I hope the president stays strong.”

Nor will there be much surprise with labor’s opposition.

AFL-CIO President Richard Trumka is calling on Congress “to reject any cuts to Social Security, Medicaid, or Medicare benefits, regardless of who proposes them.”

That “regardless-of-who-proposes-them” stance is spreading. Rapidly.

Ohio Senator Sherrod Brown calls Obama’s “chained-CPI” proposal “terrible.” Illinois Congresswoman Jan Schakowsky, an Obama campaign co-chair, says: “I hope that offer…will be reconsidered.” A frustrated Schakowsky said what every Democrat must if the party is to retain its image as the defender of Social Security: “This should be off the table.”

A lot of Democrats, many with close ties to the president, are saying the same thing.

Congressional Progressive Caucus co-chair Keith Ellison, the Minnesota Democrat who was one of Obama’s earliest and most enthusiastic backers in 2008, did the math: “The current average earned benefit for a 65 year old on Social Security is $17,134. Using chained CPI will result in a $6,000 loss for retirees in the first fifteen years of retirement and adds up to a $16,000 loss over twenty-five years. This change would be devastating to beneficiaries, especially widowed women, more than a third of whom rely on the program for 90% of their income and use every single dollar of the Social Security checks they’ve earned. This would require the most vulnerable Americans to dig further into their savings to fill the hole left by unnecessary and irresponsible cuts to Social Security.”

Ellison’s bottom line: “I am committed to standing against any benefit cuts to programs Americans rely on and tying Social Security benefits to chained CPI is a benefit cut.”

Joining Ellison in opposition were other House Democrats who played critical roles in getting Obama elected in 2008 and reelected in 2012, including Schakowsky, California Congresswoman Barbara Lee and Michigan Congressman John Conyers, who says: “Any debt deal that cuts Social Security, Medicare, or Medicaid benefits is unacceptable.”

For Obama, these voices are significant. He is losing the allies who should be in the forefront of the fight to seal any deal he reaches with House Speaker John Boehner, R-Ohio. Without a solid base of Democratic votes in the House and Senate for it, this deal won’t be done.

And make no mistake: a fiscal-cliff compromise that compromises Social Security should not be done. Period.

That’s the message coming from the Progressive Change Campaign Committee, which as usual has moved rapidly — and effectively — to build mass opposition to a cut that will only happen if Americans are unaware of the threat.

Former US Senator Russ Feingold’s group Progressives United has partnered with MoveOn.org and leading progressive groups to develop a “whip count” that names the names of Senate Democrats who are “Weak-Kneed,” who are “Part-way there, or Wavering,” and who are “Champions” committed to opposing any deal that cuts Medicare, Medicaid, and Social Security benefits.

The president has placed himself in the “Weak-Kneed” camp.

Congressional Democrats should not stumble with him.

As Senator Jeff Merkley, D-Oregon says, “We had an election, and the voters sent a message to Congress to focus on jobs and fairness—not cutting benefits for people who have worked all their lives and are now making ends meet on fixed incomes. The formula we use to adjust cost-of-living changes for seniors needs to reflect the real costs they face, not the budgetary fantasies of Washington.”

No matter who is peddling those fantasies.

Low-income, elderly women will be the hardest hit by benefit cuts. Check out Bryce Covert’s coverage here.