Answer:
He is assuming that the professors are hiding some involvement with the communist party.
Step-by-step explanation:
An assumption is a mistrust about something. This assumption has no evidence to prove it, but it does have some elements that cause it to be established through mistrust.
In the text shown in the question above, we can see that the author of the text is assuming that professors at the University of Washington are hiding the involvement they have or have had with the Communist Party. This is because he is suspicious of the teachers 'refusal to answer the investigators' questions about the political involvement they have. For the author of the text, the teachers refuse to answer the questions because they do not want to reveal their positions in favor of communism.