PHILADELPHIA (Reuters) - It should have been a triumphant night for Hillary Clinton when her rival Bernie Sanders gave a rousing speech urging his supporters to vote for her in the Nov. 8 U.S. presidential election.

Instead it turned into a sign of potential trouble for her White House bid. His speech on Monday to the Democratic National Convention in Philadelphia urging the party to unite against Republican Donald Trump was met with some jeers when he endorsed Clinton – a sign he had lost control of his own movement.

“I’m beyond disappointed,” California delegate Aleece Depuey, 49, said after Sanders sought to rally support for his one-time rival.

Hundreds of Sanders supporters marched through the streets on Day One of the four-day convention, chanting: “We want Bernie!” Delegates wore “Bernie or Bust” buttons. Others donned Robin Hood-style hats, a call to redistribute wealth from the rich to the poor.

When he spoke, a scuffle broke out between a Sanders supporter and a Clinton supporter in the hall.

The backlash raised questions over whether - and how - Clinton could ever win over Sanders supporters.

With opinion polls showing the Clinton-Trump race tightening, Clinton needs Sanders’ voters more than ever. Sanders, a U.S. senator from Vermont, arrived in Philadelphia with 1,894 of 4,763 delegates after winning 13 million votes in the Democratic nominating contest.

To many of Sanders’ backers, Clinton is a bridge too far. They see her as the kind of political insider, backed by reams of corporate money, that drove them to Sanders and his fight to rein in Wall Street and remove income inequality. Others simply do not trust her, opinion polls show.

In a Reuters/Ipsos poll released at the end of June, some 15 percent of Sanders’ backers said they would vote for Trump, and 19 percent would support neither Clinton nor Trump.

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Sanders won the states of Colorado, Indiana, Michigan, and New Hampshire in the run-up to the convention, and nearly won Iowa - all states that could be closely contested by Trump in the general election. Clinton likely will need some portion of Sanders’ support to stay competitive in those states.

‘HILLARY FOR PRISON’

Clinton’s campaign had hoped in Philadelphia to put the bare-knuckle primary fight behind it, but Sanders’ voters were enraged by Friday’s embarrassing release of internal party emails by the activist group WikiLeaks showing party officials clearly favored Clinton over their candidate.

Sanders supporters seemed to be everywhere, often with a bigger presence than Clinton supporters, a jarring sight at an event where she is due to be formally nominated as the party’s presidential candidate.

At a delegate welcoming event on Sunday night, shouts of “Bernie!” filled the air as his supporters circulated a petition to force convention organizers to hold an extended roll-call vote on the floor this week that would require each delegate to declare his or her support.

Others pledged to contest Clinton’s choice of Democrat Tim Kaine, a U.S. senator from Virginia, as her running mate.

When at mid-day Sanders addressed more than a thousand of his delegates at the city’s convention center, the crowd erupted in fury when he asked them to switch their allegiance to Clinton.

“Brothers and sisters,” he said over their jeers, “this is the real world that we live in. Trump is a bully and a demagogue.” People started shouting back: “So is Hillary!”

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Sanders did not mention Clinton again. But he already had lost the attention of some of his most fervent fans.

“As soon as he said back Clinton, everyone stopped listening,” said Cindy Melchert, a protester who listened to the appeal over a loudspeaker at a local park.

A Michigan native, Melchert said she would not vote for Clinton in November under any circumstances. For her, the movement now was less about Sanders and more about showing the Democratic National Committee “they had us and absolutely lost us.”

Another protester, Michael Arnold of Atlanta, would not have been out of place at a Trump rally, sporting a T-shirt that read “Hillary for prison.”

SEEKING DECORUM

Fearing a similar scene on the convention floor would embarrass Clinton, Sanders’ campaign emailed delegates before Monday night’s program, urging them to restrain themselves.

“Our credibility as a movement will be damaged by booing, turning of backs, walking out or other similar displays,” it read.

Some Sanders supporters appeared willing to set aside their qualms about Clinton, largely out of a desire to see Trump defeated in the election. Diana Hatsis-Neuhoff, a delegate from Florida adorned with buttons backing Sanders, said she planned to vote for Clinton in the general election.

“Yes,” she said, “we’ll hold our nose and vote.”

Others felt their fellow Sanders supporters had taken the movement too far. “We are surrounded by people who are so selfish and so self-absorbed,” said Melissa Robbins, who worked for the Sanders campaign in Philadelphia. “Not voting for Hillary is a sure win for Donald Trump.”

But that may not be enough to sway Sue Spicer from Indiana, who said she had trouble imagining voting for either Clinton or Trump. “It’s hard to feel they have our best interests in mind,” she said.