This strikes as starting from the conclusion you want to reach (current funding cuts are bad) and then trying to build a narrative to prove it.

Post-WWII the US had already become the superpower in science and technology and Europe was struggling to rebuild after the war (e.g. rationing ended in the UK only in 1954).

The brain drain started before the war, was amplified by the war, and continued after the war because the US were so rich generally. This has continued since. I don't think that what Trump is doing will have an impact because it may not last and the US will still overall much more attractive than, say, Europe.