Let’s say that at the end of the day, liberals face a choice: Which is worse, extended sequestration or a Grand Bargain that cuts Social Security and Medicare in exchange for new revenues, as Obama’s forthcoming budget seems designed to secure?

In an interview with me today, Dem Rep. Raul Grivjalva — the co-chair of the Congressional Progressive Caucus — told me he would vote No on any Grand Bargain with entitlement cuts like Chained CPI for Social Security. And he said that if we face the theoretical choice outlined above, the sequester is the better, or least bad, option — because ultimately the sequester could be changed under pressure from public opinion, while entitlement cuts would be harder to undo.

“I really believe that the sequester itself would start to unravel under public pressure,” Grijalva told me. “Let’s let the political and fiscal consequences of the sequester take hold with the American public. I’d rather count on the public changing the sequester than on cutting a deal that exposes Social Security into the future.”

Asked if he would vote against any deal containing Chained CPI, Grijalva said: “I’ve made the commitment that if this is part of it, I will not vote for it. I can’t support it.”

However, asked if he thought a sizable bloc of liberals would vote No, Grijalva demurred, and — in something that will bring back bad memories for the left — cited the health care debate as an example. “At this point, I don’t know,” he said. “We’ve been through this before with the public option. The motivation will be there to close ranks and support the president.”

A number of liberal groups have harshly criticized Obama today over his Chained CPI proposal. This is exactly what they should be doing; I, too, oppose Chained CPI and see it as horrible policy. However, it is still unclear to me how this ends, other than in a choice between extended sequestration and a deal to avert it. This isn’t to say liberals need to make a choice right now. As Bernie Sanders has urged, we don’t need to accept this frame — certainly not at this point.

But down the line, it may be a choice we do face — we should be realistic about this possibility — and if the sequester is later seen to be the least bad option, we’ll need to spell out why this is the case. As Grijalva has now done today.