Left-Wing Supporters Boo as Bernie Sanders Says 'We Must Elect Hillary Clinton'

Supporters of Sen. Bernie Sanders booed today as the former Democratic presidential contender told them, "We must elect Hillary Clinton."

He was appearing for the first time this week in Philadelphia, where the Democratic National Convention is set to kick off later today.

Addressing a group of his delegates at the Pennsylvania Convention Center, Sanders spoke broadly about his accomplishments during the primary battle.

However, when he said that Hillary Clinton -- his primary season rival who is now the presumptive Democratic nominee -- must be elected, the crowd began booing.

Attempting to take back control of the room, Sanders said, "Brothers and sisters, this is the real world that we live in," and argued that Donald Trump is too "dangerous."

From there, the crowd began chanting, "We want Bernie!"

After Sanders finished speaking, a whispered exchange between the Vermont senator and his wife was picked up by a hot microphone. According to ABC News producers at the venue, it sounded like Jane Sanders told her husband, "They don't know your name isn't being put in nomination." But there are some reports that she said "is" instead of "isn't."

The Sanders campaign has not yet replied to ABC News' request for comment or clarification. But campaign spokesman Michael Briggs told the Guardian that Jane Sanders “means there will be a roll call vote and the senator’s name will be placed in nomination,” perhaps deflating fans of the Vermont senator who read palace intrigue into his spouse’s remarks.