The 185,000-strong nurses union threatens unrest at July’s presidential nominating convention in Philadelphia

The 185,000-strong National Nurses United is the scrubs-wearing symbol of a split in the Democratic Party that threatens to inflict damage at the presidential nominating convention in Philadelphia.

While Hillary Clinton tries to bring the nomination battle to a close and unite the party before the general election showdown with presumptive Republican nominee Donald Trump, the nurses are having none of it. They are looking for a fight.

On a desk at the union’s headquarters here sits a gag gift called “The Hillary Clinton Voodoo Kit,” complete with pushpins and a miniature doll. “Stick it to her before she sticks it to you!” the cover reads.

Seeing a visitor eyeing the kit, RoseAnn DeMoro, executive director of the nation’s largest nurses union, smiles and says: “Don’t write about that.”

The nurses aren’t deterred by delegate math showing Mrs. Clinton with an all-but-insurmountable lead over Sen. Bernie Sanders. Nor are they much interested in smoothing over rifts. With at least 150 nurses set to attend the convention as pro-Sanders delegates, they will travel to Philadelphia for one last effort to land him the nomination.

“I’m not going there with any intent except to get Bernie Sanders elected,” said Sue Phillips, a critical-care nurse in the San Diego area who will be a delegate. 

About the best Ms. DeMoro can say about Mrs. Clinton is that if she becomes president, her administration would be “less racist” than that of Mr. Trump. She predicts Mrs. Clinton would lose in November.

Malinda Markowitz, a nurse and union official, helped scoop ice cream last week for students who showed up at a Sanders event at the University of California, San Diego. The Democratic Party, she said, “has been a huge disappointment.”

“They just assumed that people are going to follow what they think is right. And that’s not happening because it’s clear that Bernie is the choice of the people, it really is,” Ms. Markowitz said.

The nurses want the party to embrace a single-payer, government-run health plan that Mr. Sanders backs and Mrs. Clinton opposes. Nurses heading to the convention said they plan to join demonstrations there aimed at wringing a commitment from the party for such a sweeping overhaul.

It won’t be easy.

The Sanders campaign recently put forward Ms. DeMoro to serve on a convention subcommittee involved in drafting the party platform. She would have been a voice for making the government-run health system a policy goal.

But Democratic National Committee Chairwoman Debbie Wasserman Schultz left Ms. DeMoro off the panel, according to convention officials and Sanders campaign aides. An aide to Democratic convention planners said Ms. DeMoro was excluded because of the limited number of committee spots and a need to create diverse memberships.

One official who hopes to bridge differences between the nurses and the Clinton campaign is California Sen. Barbara Boxer. A Clinton supporter, the senator said she has ties to the nurses and predicted they would line up behind Mrs. Clinton when she wraps up the nomination.

“At the end of the day, the nurses will come home to Hillary,” Ms. Boxer said. “It’s too soon for them right now.”

For all their expertise in the healing arts, nurses are no strangers to political combat.

Ms. DeMoro was part of a nurses union effort in the mid-2000s that helped thwart then-California Gov. Arnold Schwarzenegger’s plans to rein in state spending and scale back the political clout of public employee unions.

The nurses trailed Mr. Schwarzenegger, protesting his appearances and calling for the defeat of the ballot measures he promoted. When voters shot down the measures, the nurses celebrated with a luau where they served a stuffed pig and formed a conga line, singing: “We are the mighty, mighty nurses.”

Over the past decade they haven’t mellowed much. In their latest campaign, the nurses have spent $4.2 million promoting the Sanders candidacy, much of in California, which holds its presidential primary next Tuesday.

The union aired radio ads and posted Sanders billboards. They filled a customized bus as it traversed the San Diego area last week to stump for the Vermont senator. Actress Rosario Dawson and Ben Cohen of Ben & Jerry’s ice cream dished out Cherry Garcia scoops at stops, aided by nurses in bright red Sanders shirts. Later, the bus stopped at a medical center to greet fellow health care workers making a shift change with burritos and Sanders campaign memorabilia.

“I need a button,” a nurse in scrubs told the group.

A surgeon walked past and took a Sanders sign to post at home.

On the bus, singing Dionne Warwick’s “Do You Know the Way to San Jose,” the nurses seemed cold to Mrs. Clinton’s call for unifying the party. On the same day, Mrs. Clinton spoke to the United Food and Commercial Workers union in Las Vegas and called on Mr. Sanders’s supporters to set aside grievances and coalesce behind her candidacy.

“I look forward to coming together to unify our party to stop Donald Trump and move our country forward,” Mrs. Clinton said.

The nurses wouldn’t mind the party unified—so long as Mr. Sanders is at the top of the ticket. But if he falls short, what would they do?

“You know what I’m thinking now? Bernie is going to win. Nurses do not give up on our patients, and we are not going to give up on Bernie,” said Dahlia Taiag, a recovery-room nurse.