At an MSNBC town hall on Thursday, Chuck Todd asked Senator Bernie Sanders about a radio interview in 2011 in which he agreed that it might be a good idea to primary President Obama for the 2012 party nomination.

For weeks, Hillary Clinton and her surrogates have raised the issue of Sanders’s flirtation with a primary challenge, and so it was odd that Sanders didn’t have a better response ready. He characterized his comments as an offhand answer to a radio-show question, which isn’t true. He brought up a primary challenge several times in the summer of 2011. Sanders asked rhetorically if he was “allowed” to disagree with the president and mentioned the Trans-Pacific Partnership trade pact, which had nothing to do with his 2011 endorsement of a primary for Obama.

Sanders has a much better case to make, and for some reason he hasn’t fully made it. He had a very specific reason for suggesting a Democratic primary in 2012: In debt-ceiling talks with Republicans, Obama proposed cutting Social Security benefits and raising the Medicare age to 67. After initially refusing to negotiate over the debt ceiling, the White House pivoted to a full-scale embrace of austerity in the hopes of taking away the Republican Party’s main talking point ahead of the 2012 election.

Sanders was one of many members of Congress standing athwart this rush to austerity, though he did go further than any of his colleagues by suggesting a primary. His remarks were only a minor news story at the time, but the basic dispute is now mapping onto the entire Democratic primary, which has become a battle between progressives who are preoccupied with immediate constraints and compromise and those who seek to change the terms of debate using grassroots pressure.

Obama actually proposed more deficit reduction in the summer of 2011 than Republicans were asking for—$4 trillion instead of the $2 trillion the GOP had been requesting—and at times the White House was reportedly willing to raise revenue only through closing tax loopholes. That meant in addition to the safety net cuts, the Bush-era tax cuts would either be locked in or even lowered in some cases.

This was a monumental diversion from Democratic Party principles. For years, Democrats ran for office on promises not to cut Social Security and Medicare. They railed against the Bush tax cuts in every election cycle since the tax package was enacted. Republicans already enjoyed bashing Democrats for supposed safety-net cuts; one of the most frequently run advertisements of the 2010 midterms noted the Affordable Care Act cut $700 million from Medicare. (These cuts were mainly on the provider side and did not affect benefits, which was never mentioned in the ads.)

Aside from being potentially catastrophic politics, the Social Security and Medicare cuts were bad policy. Increasing the Medicare age would have lowered federal health spending but increased overall health spending by much more, and would have left many seniors uninsured. Obama’s method for reducing Social Security benefits by changing the Chained-CPI formula would have resulted in fairly minimal long-term budget savings but would have cost the average senior $28,000 by age 95.

Progressive groups, already rankled by the White House undermining the public option and mounting only a light push for the cap-and-trade climate bill in the House were apoplectic, particularly groups dedicated to protecting the safety net. “There was an enormous amount of frustration,” recalled Alex Lawson, executive director of Social Security Works.

A large majority of Democrats in Congress shared the frustration. Upon news of one Obama debt-ceiling proposal that didn’t raise the Bush tax rates, Senator Barbara Mikulski told The Washington Post “it was like Mount Vesuvius…. Many of us were volcanic.”

It was the most serious breach to date—and since—in the relationship between Obama and his base, both in Congress and beyond. The deal never happened, because Republicans walked away, though it was unclear enough Democrats supported the grand bargain anyhow.

But it was in the middle of negotiations when Sanders mused about a primary challenge. It first came up on a Thom Hartmann show, when a caller vented about the debt-ceiling talks. After his remarks circulated, Sanders expanded his thought process on C-SPAN’s Newsmakers:

“Here’s the point: If you’re asking me, do I think, at the end of the day, that Barack Obama is going to be the Democratic candidate for president in 2012? I do. But do I believe that it is a good idea for our democracy and for the Democratic Party—I speak, by the way, as an independent—that people start asking the president some hard questions about why he said one thing during his previous campaign, and is doing another thing today on Social Security, on Medicare. I think it is important that that discussion take place.”

The episode is a Rorschach test for Democrats. Clinton supporters clearly look at Sanders’s remarks and see a disloyal sometimes-Democrat who will pick up his ball and go home when tough compromises are at hand. Many of the same center-left pundits who are now blasting Sanders for being unrealistic were writing in 2011 about how Democrats would have to suck it up and accept Social Security cuts.

Sanders represented the other view—that there were certain red lines Democrats shouldn’t cross, and that elite opinion had wandered far astray from where most voters actually were. “What [Sanders’s] point was, really clearly, was that there needs to be a progressive alternative that is clarion and clear that people can understand, and that the counterpoint would be to the Tea Party, which was pulling the entire debate to the far right at that time,” said Lawson.

What happened since has 2011 has left many progressives feeling like Sanders was vindicated. “What Bernie Sanders was describing then is exactly the dynamic that is working out positively for Democrats now, which is a race to the top on popular economic populism issues,” said Adam Green of the Progressive Change Campaign Committee. “He wasn’t proposing defeating President Obama, he was proposing moving President Obama in a more economic populist direction. It’s what we’ve had in the primary, and what we had more of in Obama’s second term.”

Regardless of where you come down on the question, the context here is important and should be discussed whenever this episode arises, which it surely will again. Too often the media has described it as Sanders’s having had very general objections to the  Obama presidency. (“But there are some Democrats who want to continue the president’s policies. Why should they trust you as somebody who wanted him primaried?”was Chuck Todd’s formulation on Thursday.) It was about much more than that.