Voters’ convictions can shift quickly as political circumstances change. Sanders supporters view Clinton as their opponent now, but once the general election arrives the battle lines will be re-drawn and that is likely to impact voter loyalty. “We don’t like to think of ourselves as contradictory and inconsistent, but we are,” said Lilliana Mason, a political science professor at the University of Maryland College Park. “When we’re in the middle of a fight, it’s really hard for us to imagine joining the other team. But who we identify with can change quickly when our attention shifts to a different fight.”

People tend to vote according to partisan affiliation in general elections. Of course, Sanders has done well with independent voters. But since many of those voters align with a particular party, the left-leaning ones are still likely to vote Democratic in the general election. “For many Sanders supporters there will be an early stage of grief, then there might be denial and anger,” Nalder said. “It takes a while before people get to acceptance.”

None of this is to say that voters who make a vow never to vote for Clinton won’t stick with it. They could write Bernie’s name in during the general election if she wins the nomination. They could vote for another candidate apart from Clinton, or decide to stay home. There will also be voters who emerge from the election with a far worse opinion of the Democratic Party. “When I voted Democrat for Barack Obama, I didn’t feel like the party was as corrupt as I feel like it is today,” said Bailey Osborne, a 54-year-old Bernie supporter from Burlington, Vermont, who says she is currently registered as a Democrat. “Now I feel absolutely no loyalty to the party.”

As the race drags on, some Sanders supporters feel frustrated by pressure from friends and acquaintances who want them to vote for Clinton if it comes to that. They argue that Sanders is a stronger candidate, pointing to polling indicating that he would be more likely to defeat Trump, despite the fact that early predictions of general-election matchups are unlikely to act as a reliable gauge of how candidates might fare. “People are acting like we want to throw the election, and that’s not the case at all,” Osborne’s 22-year-old daughter Casey said. “They say our unwavering support is a bad thing, but I think it’s a testament to the sort of loyalty he inspires. The reason that we are unwavering is that Bernie Sanders is a stronger candidate than Hillary. If anything it should be Clinton supporters that switch sides to Sanders.”

Sanders has made it very clear that he believes Trump must be defeated, promising to do “everything in my power to make sure that no Republican gets into the White House.” He has also vowed not to mount an independent presidential bid. But if he doesn’t win the nomination, Sanders has indicated Clinton will have to work hard to win over his supporters. “I can’t snap my fingers and tell people what to do,” Sanders told ABC News in a recent interview, adding: “If Secretary Clinton is the nominee, she is going to have to make the case to the American people, not just to my supporters, but all Americans.”