"Election days come and go, but the struggle of the people to create a government which represents all of us and not just the 1%, a government based on the principles of economic, social, racial, and environmental justice, that struggle continues," he said.

But Sanders also delivered a full-throated endorsement of Clinton's candidacy, saying she would make an "outstanding president."

"Based on her ideas and leadership, Hillary Clinton must become the president of the United States," he said.

He commended the former secretary of state's current positions on wages, the cost of college, and health care. And he said the high stakes surrounding the Supreme Court should keep people from sitting on the sidelines.

"If you don’t believe this election is important, if you think you can sit it out, take a moment to think about the Supreme Court justices that Donald Trump would nominate and what that would mean to civil liberties, equal rights and the future of our country," he said.

Clarissa Rodriguez, a pro-Sanders 17-year-old from Texas, was one of those voters who is disappointed with the outcome of the primary, including decisions by Sanders and Warren to endorse the presumptive nominee. While she said she's 90% sure she'll come around and vote for Clinton, she's not happy about it.

"I can tell you for sure that I’ll be holding my nose for the election," she told us.

Clinton is expected to formally secure the nomination in a roll call vote of the states Tuesday afternoon. She will address delegates on Thursday, the final night of the convention.

Watch the remarks made by Sanders below: