President Trump issued an executive order Monday restricting federal funding for research that involves a controversial field of scientific study known as "gain-of-function" research.

The research, which is also known as "dual-use" research, involves experimenting with viruses and other pathogens that have the potential to trigger a pandemic. Those studies could discover how infectious agents might become more transmissible or make people sicker.

This field has long been controversial because of fears that scientists could make a more dangerous pathogen in their lab that could get out and cause a pandemic. Those concerns have led to many efforts over the years to more tightly monitor and control this research.

But gain-of-function research became especially controversial and politically polarized during the COVID-19 pandemic. One theory for how the pandemic started says that the SARS-CoV-2 virus, which causes COVID-19, spilled out of a Chinese government laboratory in Wuhan, China.