It was a bold claim, and it drew applause from the audience at Joe Biden’s Ottumwa, Iowa, campaign event in early June. “I promise you if I’m elected president … we’re gonna cure cancer,” said the former vice president and current Democratic presidential hopeful. It’s a personal battle for Biden, who lost his son Beau to brain cancer in May 2015. Increasingly though, it’s also political.

If opposition to President Donald Trump’s rejection of the Affordable Care Act unites the Democratic party, rare diseases — which include many cancers — are now dividing the party’s lineup of presidential candidates as they begin weeks of intense, televised debates. This divide is emerging as the latest proxy for the tussle within the Democratic Party over how to view big industry: as a potential ally or with innate suspicion.

Biden — who is leading polls — has promised that if he’s elected, he will bring back full funding for the 21st Century Cures Act that he had helped lead through Congress as vice president and touted on the Democratic debate stage last week. The Trump administration has withheld funds meant under the law for the National Institutes of Health (NIH) to expand research on rare diseases — which fewer than 200,000 people are diagnosed with. The law also amends FDA regulations to allow for companies to — in some cases — seek expedited drug approvals without clinical trials, simply by providing other data that points to success. Among presidential hopefuls, Biden, Sen. Kirsten Gillibrand, Sen. Amy Klobuchar, Sen. Cory Booker, former Rep. Beto O’Rourke and Rep. Eric Swalwell have supported the law.

[The 21st Century Cures Act contains] provisions that put patients at risk for the sake of corporate profits. Saloni Sharma, Warren campaign spokesperson

Klobuchar, who is co-chair of the rare diseases caucus, and Swalwell, also on the caucus, have pushed another bill, the Orphan Products Extension Now Accelerating Cures and Treatments Act — better known as the OPEN Act. It would extend the exclusivity period for rare disease drugs — currently five years — by an additional six months. During this period, no other company can sell that drug, irrespective of whether it’s patented. Another Swalwell-backed bill, the Advancing Access to Precision Medicine Act, would facilitate customized genomics-based treatment for rare diseases. Neither has moved in this Congress.

But Sens. Elizabeth Warren and Bernie Sanders — two of the most prominent Democratic candidates — are opposed to such bills, which they argue would allow pharma companies to profit by short-circuiting scientifically established procedures and rushing drugs to the market. Warren voted against the 21st Century Cures Act in 2016.

The law includes “provisions that put patients at risk for the sake of corporate profits,” says Saloni Sharma, spokesperson for Warren’s presidential campaign.

In all, between 25 million and 30 million Americans — at least one in every 12 citizens — suffer from rare diseases, according to the NIH, making them an important voting bloc. An estimated 1.7 million Americans were diagnosed with different types of cancer in 2018 alone. This debate is pivotal for them, but there are no easy answers on whether these bills would help patients of rare diseases, or increase the chance of them being exploited.

Fundamentally, the argument revolves around the need to incentivize research and development into potential cures for these diseases, in the hope that this will lead to much-needed drugs. “Beto co-sponsored the bipartisan effort to pass the 21st Century Cures Act because it would encourage innovation in medical research and development, modernize clinical trials to make the review and testing process more efficient … and help new treatments reach patients more quickly,” his campaign said in a statement.

One key challenge researchers often come up against involves clinical trials. In the case of many rare diseases, there are just not enough potential candidates available to meet the minimum requirements of a standard clinical trial prescribed by the FDA. But without FDA approval, no drug can enter the market. By allowing other evidence instead, as the 21st Century Cures Act does, researchers can get around this dilemma. Swalwell supports “massive investment in genomics, data-sharing and targeted therapies so we can find cures in our lifetime for diseases that affect millions of Americans,” says Caitlyn McNamee, press secretary of his presidential campaign. “That would certainly include finding cures and treatments for upwards of 25 million Americans living with a rare disease.”

But critics such as Warren and Sanders argue that opening up these regulations risks giving Big Pharma room to take advantage of patients. By introducing drugs that haven’t been through the most rigorous of clinical trials, these firms risk patient health, they argue. And with longer periods of exclusivity, these firms can also monopolize the market of a key drug patients need — enabling them to set higher prices than would be the case in a competitive market.

Some presidential candidates find themselves torn between the two sets of arguments. Take Booker, whose state of New Jersey is home to 14 of the world’s 20 largest pharmaceutical companies. In 2014, he raised more money from the pharma industry than any other senator, according to the nonpartisan Center for Responsive Politics. But despite his support for the 21st Century Cures Act, Booker in January took on Big Pharma, questioning the “outrageous and unjustifiably high cost of prescription drugs” in a joint press conference with Sanders.

Klobuchar championed the OPEN Act but then backtracked before recently once again backing the proposed legislation, says health care attorney Candace Lerman. “The whole thing caught everyone in the rare-disease-advocacy community by surprise,” says Lerman.

At the other end of the Democratic Party spectrum, Warren’s campaign is also cautious about not appearing opposed to finding cures for rare diseases under the 21st Century Cures Act. Her campaign insists that the final bill includes several of her legislative proposals on increased funding for medical research, but that ultimately she couldn’t look past the role of the pharmaceutical industry.

That nuance will be difficult to maintain as Democratic candidates look to distinguish themselves in a crowded lineup. As the race sharpens after the first debate, with Biden at the center of the action, an emotion-filled subplot is emerging.