On Friday, President Donald Trump signed an executive order effectively banning entry to the United States for citizens from certain Muslim-majority countries. The ban could have massive ramifications for science, and scientists — like computational biologist Samira Asgari, for example, who was stopped from boarding a flight in Frankfurt on Saturday morning. The executive order that Trump signed Friday night is ostensibly to “protect the American people from terrorist attacks by foreign nationals” from Iran, Iraq, Libya, Somalia, Syria, Sudan, and Yemen.