According to research from Britain's University of Warwick, published last January, scientific migration is common, and vastly beneficial to the United States.
"Nearly half of the world's most-cited physicists work outside their country of birth," the study said.
A survey of 158 of the most highly cited physicists showed systematic migration to nations with large research and development spending, most notably the United States.
"At birth, 29.7 percent of physicists are in the USA. This increases to 43.4 percent at first degree, to 55.1 percent at PhD, and to 67.1 percent presently," the report said.
However, the number of science Nobel winners does not reflect the downward turn in the US, since the prizes are usually awarded for work done many years ago. The 8 years of very tough science funding in the US will have an impact, especially when Europe and Asia have significantly increased their funding of the sciences.