Sen. Bernie Sanders (I-VT) refused to name a single thing he admires about Sen. Elizabeth Warren (D-MA) during an appearance on CNN Tuesday, prompting chuckles from CNN’s Poppy Harlow.

Both Sanders and Warren have largely refrained from attacking each other, despite their shared status as top tier candidates in the Democrat field. There are rumblings that the two candidates have an unofficial “pact,” agreeing not to criticize each other.

However, Sanders is not going out of his way to compliment his political rival and refused to name one attribute he “admires” about Warren upon Harlow’s request.

“Everyone’s comparing you to Sen. Elizabeth Warren. You often say, ‘She is my friend.’ Let’s end with something you admire about her,” Harlow said.

“What is the thing you admire most about Sen. Elizabeth Warren as you get ready to take her on on the debate stage?” she asked.

“Sen. Warren is a friend of mine, and I admire the fact that we’ve worked together over the years on a number of issues,” Sanders said.

Anything specific?” Harlow pressed.

After a long pause, Sanders said: “No, look. We have worked together on a number of issues, and she is a very good senator,” prompting chuckles from Harlow.

Sanders and Warren – who will appear on the same debate stage in Detroit, Michigan on July 30, have not taken direct shots at each other at this point in the race. In fact, Warren praised Sanders’ Medicare for All plan during the last debate, stating: “I’m with Bernie on Medicare for All.”