I know of three strands of rocketry research that contributed to American rocketry. There was Robert Goddard's experiments with liquid-fueled rockets, as early as the 1920s, Theodore von Karman (a Hungarian who emigrated to the US in 1930) and his team at Caltech, and von Braun and the Germans.
Goddard never got significant US Government support, but he continued his experiments right up to 1940. Of course von Braun did get government support, and apparently his team learned from Goddard's experiments. The end result was that von Braun's team knew more about large rockets, and he went on to head the NASA center (Huntsville) that is most associated with rocketry, and of course to develop the Saturn V. And von Karman, of course, was the founder of JPL.
As @err4nt's comment hints at, there is a rough parallel between von Karman's emigration from Germany to the US (his family was Jewish) and Qian's emigration from the US to China.
http://en.wikipedia.org/wiki/John_Whiteside_Parsons
Happen to run into his story while reading about the history of Rocketry. His story even takes a more bizarre turn with L Ron. Hubbard, and finally his death in a mysterious explosion.
Another interesting co-founder (one of the original handful, along with Parsons) was Frank Malina, who was the second director of JPL (after von Karman).
Malina was also suspected by the FBI of having Communist sympathies. He eventually left JPL and went to live in France.
No, it wasn't. America intentionally established Operation Paperclip with the intention of recruiting German scientists. The Chinese didn't have to do anything to get Qian (and most likely weren't even thinking about space in 1950) - America just handed him to them, thanks to the US government's enormous stupidity.