Third Way Co-Founder Jim Kessler on Friday explained the group’s Monday op-ed in the Wall Street Journal criticizing a plan backed by Sen. Elizabeth Warren (D-MA) to expand Social Security.

“That Social Security plan was the final moment for us,” he said in an interview on Sirius XM with Ari Rabin-Havt, as recorded by the Huffington Post. “That Social Security plan had been out there but really languishing — because Senator Warren has such a powerful compelling voice, she started talking about it, and it suddenly it became much more talked about and viable alternative.”

Kessler said that the op-ed was not meant as a personal attack on Warren, but that she gave a popular voice to a plan that concerns Third way.

“She is a very compelling elected official and national figure,” he said. “Her involvement in that particular bill, we just looked at it and said ‘okay, this seems to be starting to get out of hand.'”

The group’s op-ed incited a negative response from progressives and Warren herself. The Progressive Change Campaign Committee called on multiple Democrats to cut ties with Third Way, and Warren said the group was “flatly wrong” about its belief that Social security is insolvent.