Biologists working on controversial, cutting-edge technology say they fear what will happen if recent advances come to the attention of President Donald Trump.

Trump hasn’t made any public comments about research involving stem cells, human embryos, or gene editing. But researchers live in fear of an incendiary tweet or a sudden announcement of policies that restrict research. They feel they are at risk because of how sensitive technologies have hurtled forward during Trump’s first 10 months in office.

Just this year, U.S. researchers demonstrated a working artificial womb, used CRISPR to correct a genetic defect in human embryos, took strides toward manufacturing synthetic embryos, and moved forward with an in vitro fertilization procedure that uses DNA from three biological parents.

“Mr. Trump has not paid attention to us. It would not be good if he paid attention to us,” Gerald Schatten, a stem-cell researcher at the University of Pittsburgh, told a gathering of 130 fertility experts from 30 countries at a conference at New York’s Plaza Hotel in October.

Researchers are concerned that any one of the new advances could prompt steps by the Trump administration to limit science, similar to President George W. Bush’s restrictions on federal funding for stem-cell research in 2001.

“There is precedent here,” says Gretchen Goldman, research director for the Center for Science and Democracy at the Union of Concerned Scientists, a nonprofit science advocacy group. “We’re hearing from folks that they’re aware how politically controversial their work is.”

Worst case

Adding to scientists’ anxiety is that Trump’s views on the frontiers of biology are simply unknown. Of the president’s more than 30,000 tweets so far, none mention DNA, stem cells, or gene editing, according to the Trump Twitter Archive.

Meanwhile, Congress hasn’t held a hearing on such technology since June 2015.

“While President Trump doesn’t appear to have any strong beliefs on [these subjects], it’s clear that he’s composed a cabinet of individuals that may be less than thrilled about the prospects of such research,” says Ryan Hagemann, director of technology policy at the Niskanen Center, a libertarian think tank based in Washington, D.C.

The political atmosphere means even scientists who've made efforts to raise public awareness about new technology see the chance for trouble. Jennifer Doudna, one of the inventors of CRISPR, says she is worried that fast advances in gene-editing technology could backfire if they come to the attention of politicians in the wrong way.

“In the short term, my worst-case scenario is that somebody, somewhere, does something with CRISPR that is dangerous, or at least is perceived as dangerous or irresponsible, that leads to a big public backlash,” Doudna told a gathering of science journalists in San Francisco last month.

“Let’s say if tomorrow a CRISPR baby were to be announced—how would that be received in the current climate of the United States? I worry that this would ... cause a lot of people to call their government representatives and say, ‘What is this CRISPR? You need to shut that down.’”

Anti-science

Ten months into his presidency, President Trump has yet to choose a science advisor, the longest any modern president has taken to do so, notes the Washington Post.

In the absence of expert advice, the administration has acted in ways that many see as anti-science, including appointing Scott Pruitt, who questions man-made climate change, to lead the Environmental Protection Agency. Trump himself tweeted that global warming is “a hoax.”

More recently, the administration has taken steps to define embryos as human beings with legal rights—something that could curtail research on infertility, miscarriage, and the development of inherited diseases in human embryos.

Such language found its way into a draft strategic plan the Department of Health and Human Services released in October. A sentence saying the agency serves “Americans at every stage of life” was changed to read “Americans at every stage of life, beginning at conception.” And when congressional Republicans unveiled a 429-page tax bill on November 2, it stipulated that parents could set up a tax-advantaged college saving account for a “child in utero.”

Congresswoman Diana DeGette, a Democrat from Colorado, called the provision “a back-door attempt to establish personhood from the moment of conception.”

Postponing debate

So far, biologists have largely been shielded from Trump’s attention. Although the president early on called for slashing the budget of the National Institutes of Health by $7.5 billion, that idea hasn’t gained any political support.

The president also held onto Francis Collins, a deft administrator named head of the NIH by former President Barack Obama and one of the few holdovers to have navigated the change of administration.