limbo. >> my research was disrupted. >> reporter: dennis hu flew to shanghai in january 2020 along with friend and lab mate matthew jikelski. while matthew, an american, returned to the u.s., hu was delayed in going back to their university in boston. first by the outbreak. several attempts to return failed. then came a new policy under president trump. >> first i think it's a policy of discrimination based on nationality. >> to suspend the entry -- >> reporter: hu was referring to proclamation 10043. in may 2020, trump blocked chinese graduate students and post-grad researchers that came mostly from eight chinese universities with suspected chinese military ties. the policy singled out those studying in s.t.e.m. fields -- science, technology, engineering, and math -- framed as part of national security. >> there certainly is espionage that goes on in u.s.