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“[Obamacare] has problems, but we damn well are not going to see it repealed and have no replacement there at all,” Sanders said.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

It’s one thing for President Barack Obama to flatter the president-elect in trying to negotiate a smooth transition of power, or for Sanders to acknowledge the economic plight of some Trump voters in talking about how Democrats plan to address it. But it’s disappointing that a leading light of the opposition would speak so kindly about a man who threatens to be the most dangerous president in American history—and, worse, that Sanders would pledge to work with Trump on trade and other issues of supposed commonality—when there’s scant evidence that Republicans are up for serious collaboration.

Sanders’s play here is transparent. Because of his appeal with white working class voters, he thinks he’s well positioned to help progressives win them back. So he’s treading carefully, trying not to needlessly alienate them. But even Cuomo called out his timidity, noting that Sanders “won’t commit to voting against” attorney general nominee Jeff Sessions, despite concerns about the Alabama senator’s civil rights record, or Environmental Protection Agency administrator nominee Scott Pruitt, who denies climate change and has been a harsh critic of the very bureaucracy he’d run.

Sanders said he was “trying to be polite” by saying he’d give the nominees a fair hearing. “I’m just saying, before I vote against them, I want to hear what they have to say,” he added.

The town hall also revived Sanders’s chronic problem of prioritizing economic justice over the identity-based concerns of marginalized groups. Towards the very end, Cuomo asked the senator what he’d say to Americans who see Democrats as “more concerned with what bathroom people go into [than] how they earn a living?”

“Very fair question,” Sanders said.

But it wasn’t a fair question. It was based on a pernicious premise that the senator should have challenged. Ensuring transgender Americans can use bathrooms corresponding with their gender identities isn’t some tertiary issue. It’s a vital anti-discrimination measure. And, for transgender Americans in the workplace, it’s very much about being treated equally as they earn a living.

You wouldn’t have known this from Sanders’s answer. As always, he railed against the plutocrats, disparaging Democrats for joining with Republicans to deregulate Wall Street and pass free trade deals. “I think the American people understand that there’s something profoundly wrong in this country when you have a small number of billionaires that have so much power,” he said. He also trotted out stump-speech lines about tuition-free public colleges and higher minimum wages; with passing mentions of fighting climate change and reforming our immigration and criminal justice systems.

What Sanders didn’t do was mention bathrooms—or transgender Americans—even once.

And he wonders why critics say he only cares about economic issues.

Bernie Sanders was vindicated by last year’s general election. Trump’s victory proved that populism could win a White House race, and suggested the senator would have performed significantly better with the white working-class voters, who contributed to Hillary Clinton’s loss. He’s right to see himself as uniquely positioned to help the left rebuild.

But Sanders’s blind spots on identity politics are real, persistent, and troubling. If the senator can’t find a way to court Trump voters while also standing up to the next president—not to mention defending a broad spectrum of progressive principlesDemocrats need to find different leaders who can.