There’s some debate as to who poisoned negotiations that summer—the White House or Republicans, with each side blaming the other—but either way, the collapse of the prospective deal spared Democrats from what surely would have been a bitter internal reckoning over entitlements.

“Had the speaker taken the deal, it’s likely that debate inside the Democratic Party would have become a real battle,” says Matt Bennett, senior vice president at the centrist Democratic think tank Third Way, which believes entitlement reform is an inevitable necessity. “When he walked away from the table, Boehner deferred that debate and unwittingly helped to unify Democrats as we went into 2012 and thereafter.”

Those cuts would have been anathema to liberals, and cause for revolt. When Obama later showed willingness to trim some Social Security benefits by changing the way inflation adjustments are calculated, liberals on and off Capitol Hill threatened mutiny. Senate Majority Leader Harry Reid literally tore up a proposal to end the fiscal-cliff standoff that included the change and threw the shreds into a lit fireplace in his office. “I am terribly disappointed and will do everything in my power to block President Obama’s proposal,” independent Sen. Bernie Sanders said when Obama included the Social Security tweak in the budget the White House released last April.

The issue remains sensitive to this day. A letter circulating this week among House Democrats, which urges Obama not to include the Social Security change in his next budget proposal, garnered 108 signatories as of Tuesday afternoon, more than half the caucus.