So I can imagine American allies recruiting scientists en-mass, to protect themselves from America. The US has currently demonstrated a desire to take over allies completely (Canada, Greenland), and I'm sure few know who may be next. Some scientists may have simply wished to move abroad, and also, have quite valuable skills which are restricted in some way, hence them "disappearing".
not necessarily from America. The goal #1 of the US dominated NATO for example was to prevent Germany from getting nuclear weapons in exchange for protection by US. Now with US de-facto withdrawing, Germany would have to quickly get nukes (as well as missiles to carry them) - i don't see other option for Germany here giving the environment in Europe and MidEast. So they would also need such scientists. South Korea, Japan, Australia seem to be in the similar situation too. (and everybody understands that a nuclear weapons program can't be a long multi-year endeavor - somebody will try to stop you - and so it must be very fast once started, and thus you have to have ready-to-use skills and knowledge)
No shit? Why would they have to? Is someone ready to nuke them if it turns out they’re no longer under the U.S. nuclear umbrella, or are they some special snowflakes who should have them while Iran (and most other countries) shouldn’t?