Of all the materials valued in biomedical research, embryonic stem (ES) cells and fetal tissue have gotten disproportionate attention from politicians. Because creating ES cell lines initially requires destroying a human embryo, President George W. Bush tightly restricted the use of federal funds for research on all but a few stem cell lines. President Barack Obama then made lifting those restrictions one of his first official actions after he took office in 2009.

More recently, accusations that abortion clinics were unlawfully selling fetal tissue to researchers has stoked opposition to that type of research. So far, however, members of Congress have been unable to enact any restrictions into law.

Now, biomedical researchers are wondering: How will a Donald J. Trump administration handle these ethically delicate materials?

Fetal tissue

Tissue from aborted fetuses, used both to study early disease development and in experimental therapies that transplant cells into the brain or spinal cord, figured into 184 projects that last year received about $80 million in federal funding from the National Institutes of Health (NIH). That research has faced strong opposition from some members of Congress, and some state legislators, since late last summer, when an anti-abortion group released undercover videos in which a Planned Parenthood employee discussed fulfilling research requests for fetal tissue. Alleging unlawful sale of tissue, Republican lawmakers have tried to withdraw federal funding from the organization, and launched a special panel in the House of Representatives to investigate relationships between abortion clinics, tissue procurement agencies, and research institutions.

Trump has promised to support barring Planned Parenthood from receiving federal funding. It’s not clear, however, if he’d be motivated to place a broader ban on fetal tissue research through an executive order. (The Republican Party platform states that Congress should "make it a crime to acquire, transfer, or sell fetal tissues from elective abortions for research." But platform language is often ignored once an election is over.)

Embryonic stem cells

ES cell research, meanwhile, received about $180 million in NIH funding for 250 projects last year. All rely on cell lines originally created from donated embryos left over from in vitro fertilization procedures. NIH maintains a registry of funding-eligible human ES cell lines, created through President Obama’s first executive order in office, which loosened the Bush-era restrictions.

President-elect Trump hasn’t indicated any position on embryonic stem cell research, though he has vowed to “cancel every unconstitutional executive action, memorandum and order issued by President Obama” in a plan he released in October for his first 100 days in office.

“Trump could clearly go in and reverse the president’s executive order and change NIH’s policy,” says Tony Mazzaschi, senior director for policy and research at the Association of Schools and Programs of Public Health in Washington, D.C. “The ramifications of that would be difficult to parse,” he adds. Though the reversal would remove the underpinning of the NIH registry, it might take an additional executive order to shut down federal funding for ES cell research completely, or limit it to a certain number of cell lines.

Vice president–elect Mike Pence, meanwhile, has consistently opposed ES cell research, arguing that the discovery of induced pluripotent stem (IPS) cells—reprogrammed adult cells that take on stemlike properties—make it unnecessary to take cells from embryos.

Indeed, IPS cells “have taken some of the heat off the embryonic stem cell research,” says Timothy Kamp, a cardiologist at the University of Wisconsin in Madison who works with ES cells. But they aren’t poised to replace it altogether, he says. Embryonic cells remain a “part of the tool set that we like to use to show that our finding is robust, reproducible, and not an artifact of reprogramming or keeping cells in culture,” he says. “I think it would be quite devastating to take those lines out of federally funded protocols.”

State response?

Some have suggested that if a Trump ban did come to pass, it might stimulate support for state-level funding sources. The $3 billion California Institute for Regenerative Medicine was created by a state ballot initiative in response to the Bush-era restrictions, for example, and expects to run out of money after 2020 without a new source of funding. A renewed federal ban could help the California institute’s backers make a stronger case to voters and legislators for a new injection of funds.

But many aren’t ready to speculate about a return to more restrictive funding until the new administration indicates its position. “I personally would be very surprised if reason doesn’t prevail here,” says stem cell biologist Ali Brivanlou at Rockefeller University in New York City, who worked with embryonic stem cells throughout the Bush administration. “I have seen this movie 16 years ago,” he says. “I would be very shocked if it happens again.”