The correct answer to this open question is the following.
Although there are no options attached or further context, we can say the following.
Feklisov's rationale for American assistance to the Soviets was that the United States government was interested in the scientific minds and technology developed in the Soviet Union. So helping some Soviets coming to America, the government could learn about the secrets behind Soviet weaponry and technologies.
Let's have in mind that these were the times of the Cold War, in which the United States and the Soviet Union competed in the arms race, the space race, and in the spreading/containment of Communism around the world.
Colonel Alexander Feklisov (1914-2007) was a Soviet spy who has a legal residency in the United States.