Liberal Democrats challenged President Obama on Tuesday over his willingness to cut Social Security benefits.

At a meeting that lasted just less than 90 minutes, Obama was peppered by questions from Sens. Tom Harkin (D-Iowa) and Bernie Sanders (I-Vt.), among others, who challenged Obama on adopting “chained CPI” — a less generous formula for adjusting benefits under Social Security and other programs for inflation.

Obama has said he is open to chained CPI as part of a “grand bargain” that would include spending cuts as well as new revenue. And he didn’t back down from that support during a closed-door meeting with Senate Democrats, despite pushback from Harkin and Sanders.

“We don’t want to start whacking away at Social Security . . . or Medicare or things like that, which we have pathways to get out of this one without putting it in some kind of a grand bargain that pulls the rug out from our elderly or our sick, our needy, so we were cautioning about that, about being careful about this grand bargain,” Harkin said after the meeting.