from 50 million facebook users. one senate republican who hired the firm in his race says he doubts his campaign benefited from the facebook breach. >> they had a very limited interaction with them. i doubt it. we made it very clear if there was anything that was either unethical or illegal, it was inappropriate, we don't accept it with anybody on our campaign. >> reporter: cambridge analytica has denied those russian contacts, but congressional officials in both parties do want to hear from some of these cambridge analytica officials before their committees talk to them under oath. and one person also facing growing congressional scrutiny, wolf, as mark zuckerberg, the head of facebook. republicans and democratic lawmakers say he needs to come to congress, explain exactly what happened here in the breach of some 50 million people's facebook profile, their private information. they want to hear from him, under oath. the question is, will he agree? and if he doesn't, will they subpoena him? wolf? >> manu raju reporting for us up