I can only speak about Kennan - basically his reports and telegrams from his time in Moscow basically convinced the US government that the USSR was expansionist and a danger to the US.

His reports were the primary driving force that led the US to have a negative attitude towards the USSR and that they needed to contain it. That basically kicked off the cold war and we continue to feel the effects of until today.

He then eventually changed his mind and became very vocal against US foreign policy towards the USSR (basically the same policies that he recommended).