In June 2025, the International Society on Thrombosis and Haemostasis (ISTH) will convene its annual congress in Washington, DC — a gathering that has long exemplified global scientific exchange. However, this year, international attendees are being urged to take unusual precautions. The society’s recent travel guidance advises participants to limit personal data on devices, edit social media profiles, and consult immigration attorneys1, which align with recommendations from other countries for individuals traveling to the USA2. These precautions, although framed as practical, are a sobering indictment of the current political climate in the USA. They suggest a country that is becoming an increasingly hostile environment for international scholars, and is no longer unequivocally committed to open scientific exchange3.

The USA has historically served as a hub for biomedical research, home to leading academic institutions, National Institute of Health (NIH)-funded laboratories, and major scientific conferences. However, the very infrastructure that sustains global scientific cooperation is being threatened by rising political nationalism, suspicion of foreign influence, and the weaponization of immigration enforcement4. These shifts are not merely bureaucratic — they are ideological, and they are redefining who is permitted to participate in the scientific enterprise.