Sen. Bernie SandersBernie SandersFormer Sanders press secretary: 'Principal concern' of Biden appointments should be policy DeVos knocks free college push as 'socialist takeover of higher education' The Hill's 12:30 Report — Presented by Capital One — Giuliani denies discussing preemptive pardon with Trump MORE (I-Vt.) is urging his supporters to unite behind Hillary ClintonHillary Diane Rodham ClintonHillary and Chelsea Clinton to host series based on their book 'Gutsy Women' Democrats see spike in turnout among Asian American, Pacific Islander voters Biden officially announces ex-Obama official Brian Deese as top economic adviser MORE, warning that it is the only way to stop GOP presidential nominee Donald TrumpDonald John TrumpBiden says GOP senators have called to congratulate him Biden: Trump attending inauguration is 'of consequence' to the country Biden says family will avoid business conflicts MORE

“It is easy to boo, but it’s harder to look your kids in the face who would be living under Donald Trump,” he told the California delegation during a breakfast meeting Tuesday, according to the Los Angeles Times.

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Sanders has made the rounds at the Democratic National Convention in Philadelphia, thanking supporters and urging them to back Clinton, the party's presumptive presidential nominee. He also spoke at the Florida and Wisconsin delegation breakfasts on Tuesday.

Those events come after his prime-time address to the convention on Monday, where he said he would work to continue his "political revolution" even as he pressed his supporters to back Clinton.

The speech capped a tumultuous first day at the convention, where Sanders supporters earlier booed Democratic National Committee (DNC) Chairwoman Debbie Wasserman Schultz off the stage in response to leaked DNC emails that showed party officials plotting ways to undermine the Vermont senator's presidential bid. Throughout the day, Sanders supporters also interrupted other speakers with chants.

Sanders's Tuesday appearance with California delegates — where his backers broke out in chants of support — put him face-to-face with leadership from the Bernie Delegates Network.

The organization encompasses nearly two-thirds of Sanders delegates and is actively looking at contesting Sen. Tim KaineTimothy (Tim) Michael KaineOvernight Defense: Lawmakers release compromise defense bill in defiance of Trump veto threat | Senate voting next week on blocking UAE arms sale | Report faults lack of training, 'chronic fatigue' in military plane crashes Senate to vote next week on blocking Trump's UAE arms sale Congress set for chaotic year-end sprint MORE's (D-Va.) vice presidential nomination. The group notes that it is not affiliated with Sanders's campaign.

Sanders tried to preach unity with the Clinton camp ahead of the convention, endorsing the former secretary of State and appearing with her on the campaign trail.

But some stalwart Sanders supporters, wary of Clinton, have signaled they could support Green Party presidential candidate Jill Stein instead.

Sanders warned against that at a Bloomberg Politics breakfast Tuesday.

"But I think right now — what is it, three, four months before an election — you're going to end up having a choice. Either Hillary Clinton is going to become president, or Donald Trump," he said, according to The Washington Post