PHILADELPHIA — Michael Sparks was so revolted by the idea of seeing Bernie Sanders endorse Hillary Clinton two weeks ago that he had to go to the gym to watch the speech.

"I thought if I was on the treadmill I might not have a complete breakdown when he did it," said Sparks, 43, a die-hard Sanders fan from Indianapolis.

It didn’t work. "I raged and cried the entire day," said Sparks, who has a tattoo of Sanders on his left bicep. "It mortified me. The way it looked like [Clinton] was lording over him — it was the scariest thing I’d ever seen in my life. And I’m a big horror movie fan."

I met Sparks at a "Bernie or Bust" rally Monday afternoon held outside of Philadelphia’s City Hall, where attendees protested the Democratic National Convention. Sanders’s likeness covered nearly every square foot of the rally: His glasses and hair were drawn on a raft of yellow balloons, two 80-foot-long inflatable "joints" proclaimed "the Bern," and crowds walked by wearing "Bernie Sand Wars" T-shirts.

And yet, at the same time this was all going on, Sanders himself was on the other side of town making the argument that everyone needed to help Clinton win in November — a sentiment that ran directly opposite to the purpose of the Bernie or Bust rally. Sanders was, in both a literal and political sense, far from the movement he ignited.

On one level, it shouldn’t be surprising that the Sanders movement could carry on independently of Sanders himself. After all, Vermont’s socialist senator may have invigorated the modern American left — but he certainly didn’t create it. Some of Sanders’s supporters had their roots in earlier leftist movements like Occupy Wall Street: people who have long been tired of what they see as the Democratic Party’s centrism and want to see a more aggressive progressive vision. (Some protests in Philadelphia have been tied to Occupy.)

Still, the separation hasn’t been easy. Some Sanders fans at the Bernie or Bust rally tried to rationalize the distinction between Sanders the political ideal and Sanders the politician who endorsed Clinton. But that contradiction may eventually prove too great for Sanders fans to sustain — and some may fall out of love with the candidate they once saw as an uncompromising hero of the left.

Why many Sanders supporters won’t back Clinton just because he says so

At the rally, many of the Bernie supporters were still deeply ambivalent about whether Sanders was right about the general election. Nancy Lowery and her daughter had arrived in Philadelphia after a 20-hour drive from Oklahoma City. Both were passionate Sanders volunteers and said they had spent most of the trip arguing over whether they should heed his call to vote for Clinton.

Lowery, 59, a high school teacher, agreed with Sanders that Trump had to be stopped — even if that meant voting for Clinton. But her 35-year-old daughter, Sarah Hoss, planned to vote for Green Party candidate Jill Stein, who Hoss thinks is closer aligned to Sanders’s positions than Clinton.

"The movement is bigger than [Sanders]. He’s doing what he has to do, but I can’t go for it," Hoss said.

There’s a certain logic to Hoss’s position — after all, there’s no reason that Sanders’s endorsement should necessarily compel his supporters to back Clinton. As my former Vox colleague Emmett Rensin argued earlier this month in Newsweek, "Sanders was only a vehicle for their political values. Now that he has conceded his fight for those values, he should be abandoned as a vehicle."

This is something I heard a lot at the rally. Sanders supporters said that they’d come to dislike Clinton because of her policies — not because of anything Sanders had said — and that they wouldn’t be backing her now just because he did.

"This movement is bigger than him," says Alicia Seay, 28, an organizer of the Bernie or Bust rally. "He couldn’t go that extra mile, but he allowed us to take it forward without him."

Most liberals worry about the dangers of giving Trump the White House. Many at the Bernie or Bust rally argued that one failed Trump administration would be better than giving Clinton the chance to control the Democratic Party for two terms. "Bernie is willing to fall on a grenade to stop Trump," Sparks said. "But I'd rather have four years of tyranny than eight."

To be sure, the Bernie or Bust movement is probably a small minority among even Sanders’s supporters. According to the latest Pew poll, about 90 percent of former Sanders voters plan to vote for Clinton.

But that still leaves room for some holdouts. And unlike some of the supporters of Hillary Clinton who ultimately backed Barack Obama after she lost in 2008, these aren’t traditional Democrats loyal to the party.

Some supporters are even struggling with their feelings about Sanders

Almost every rally-goer I interviewed admitted to struggling with how to square their personal affection for Sanders with his Clinton endorsement.

Most of the people I interviewed found a way to rationalize the contradiction — often by arguing that Sanders was somehow compelled to support Clinton even though he didn’t want to. "I understand some shit goes on that we don’t know about. … I can’t for one second believe he wanted to endorse Clinton," said Jodie Chapin, 19, of Olympia, Washington.

This is also how Karen Suykens and Kim Crozier, two other "Bernie or Busters," made sense of an endorsement that otherwise struck them as inexplicable. "He was required to endorse the other candidate," Suykens says. "He wouldn't have been permitted to come here had he not."

But others reacted simply by dismissing Sanders. "It’s a sellout move that’s very disappointing," said John Souza, 62, a Teamster from Fall River, Massachusetts. "He’s a sellout. It’s going against everything he's believed politically for 30 years."

On Monday afternoon, Sanders was booed during a speech to his own delegation in which he said it was time to back Clinton. Kirk Voorhees, 56, a truck driver from northern New Jersey who came to Philadelphia with his daughter, watched it at the Bernie or Bust rally.

A live feed carried instant reactions from viewers, who could write messages or respond with emojis that then flashed across the video. As Sanders went through his stump speech — talking about the need to take on the millionaires and the importance of universal health care — Voorhees's screen lit up with a flood of little blue happy faces.

Voorhees turned to me with a prediction. "Just watch: He’s going to bash Trump, and then he’ll talk about how we have to support Clinton," Voorhees said.

As if on cue, Sanders transitioned into hitting Trump. The emojis began to show little crying faces, and then a flood of tiny angry orange faces poured across the face of the phone.

Viewers began writing a series of messages:

"We want Bernie!!"

"#NeverShillary. Never."

"This man is a bought politician."

Voorhees sighed. He committed months ago to never voting for Clinton. And while he said he still admired Sanders, he said he'll never quite think of him the same way again.

"Bernie has the opportunity to take on the machine," Voorhees said. "But not the ruthlessness."