I looked up on the NCES site the numbers of students who major in the eight leading fields. They are as follows:
Majors Numbers of Students
Business...…………... 364,000
Health professions..216,000Social sciences...…..167,000
Psychology...………..118,000
Biomedical...…...…..110,000
Engineering...………...98,000
Arts............…...........96,000
Education......………..92,000
Social sciences, psychology, arts, and education are PC suspect while engineering is not. Hence, (167,000 + 118,000 + 96,000 + 92,000 =) 473,000 of 1.261 million, or 37.5%, are likely in the PC-major category; 98,000 of 1.261 million or 7.8% are in the non-PC-major (engineering) category; business, health professions, and biomedical are unclear. These total 690,000 or 54.7% of the 1.261 million students in the eight-most-popular majors.
More research needs to be done to learn how many students are in majors with different degrees of partisanship. In leading universities the slant is more extreme than in all institutions.