Almost one week out from last week’s surprise Donald Trump win, Bernie Sanders stopped by the Late Show on Monday night to chat with Stephen Colbert about what went wrong for Hillary Clinton—and to share what he thinks will be the path forward for the Democratic Party.

Sanders was greeted with “Bernie” chants before sitting across from his host. When asked how he’s doing, the senator curtly replied, “It’s been a tough week.”

Assessing what helped Trump win the election, Sanders noted that Trump tapped into the anxiety and angst many working Americans have felt for a long time—a sentiment he said the media seemed to miss. (For those interested in reading his thoughts at length, Sanders’s analysis largely echoed an op-ed he wrote for the New York Times days after the election.)

“Trump was posing as a hero of the working class of America,” Sanders said before clarifying that his victory was conditional: ”Hillary Clinton ended up with two million more votes than Donald Trump. So don’t see this as a massive success for Trump. He lost the popular vote.”

The work to be done now, Sanders said, is to figure out what’s next for his party. “The truth is, Democrats should not be losing to a candidate who insults so many people,” Sanders noted, adding that this result signifies “something fundamentally wrong” with the Democratic Party.

When asked what an “autopsy” of the Democratic Party might reveal, Sanders replied that ”the liberal elite” should no longer run the show. (When Colbert pressed him, Sanders clarified that he does not count himself as part of that group.)

Sanders noted that those “elites” are “good-meaning people,” but added that “the party has got to transform itself to be a party which, first of all, opens the door. That is a party that feels the pain of working class people, of the middle class, of low-income people, of young people. Brings people into the party.”

According to Sanders, the views Trump expressed on the campaign trail only represent a “minority” of the electorate. “The vast majority of the American people are on our side,” he said. What’s crucial now, he said, is for people to get involved in the political process.

“When millions of people stand up and fight back, we will not be denied.”