Senator Bernie Sanders made all the obligatory statements on Monday night about taking on President-elect Donald Trump. In a CNN town hall with Chris Cuomo, he called the incoming White House occupant “a pathological liar.” He vowed to oppose Trump’s plans for immigrant deportations. He said Democrats in Congress would stand strong for the Affordable Care Act, whose repeal is the first priority for Republicans.

“[Obamacare] has problems, but we damn well are not going to see it repealed and have no replacement there at all,” Sanders said.

But the town hall also revealed something concerning about Sanders, whose success in last year’s Democratic primary made him a leading voice of the left: The independent Vermont senator is letting his efforts to court Trump voters keep him from being the voice of radical resistance that progressives desperately need.

Asked at one point to say something positive about the president-elect, Sanders practically gushed, saying “any objective assessment in the last year or a year and a half, or however long it was, will tell you that Donald Trump did something extraordinary.” Praising his “perseverance,” his “very strong political instincts” and “way to connect with people,” Sanders said, “Trump took on the Republican establishment, took on the Democratic establishment, took on the media establishment, and he ended up winning the election to become president of the United States. That is an extraordinary accomplishment.”

“I give Donald Trump his due,” he added. “I think any fair-minded person has got to.”