Liberals are mounting strong criticisms of President Obama amid news that his budget will include a Social Security benefit cut — an official endorsement of a policy compromise he’s offered Republicans for years — and warning Democrats not to dare vote to cut the cherished retirement program.

A trio of progressive advocacy groups issued scathing statements Friday in response to reports that Obama’s proposal will include a policy called “Chained CPI,” which would re-index Social Security cost of living increases to a lower rate of inflation — a benefit cut the president has included in deficit offers to Republicans since 2011.

“President Obama’s plan to cut Social Security would harm seniors who worked hard all their lives,” said MoveOn.org’s executive director Anna Galland. “That’s unconscionable. It’s even more outrageous given that Republicans in Congress aren’t even asking for this Social Security cut. This time, the drive to cut Social Security is being led by President Obama and Democrats.”

Stephanie Taylor of the Progressive Change Campaign Committee accused Obama of “proposing to steal thousands of dollars from grandparents and veterans” and threatened to subject any Democrat who votes for a Social Security benefit cut to a primary challenge.

“You can’t call yourself a Democrat and support Social Security benefit cuts,” Taylor said in a statement. “The President has no mandate to cut these benefits, and progressives will do everything possible to stop him.

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