Amid talk of a brain drain, some scientists leave U.S. behind

Academics must get and maintain grants to survive. With money, they can attract students and researchers. Without money, they'll fail to get tenure or (usually) become irrelevant to the field. Take the money source away, and they have to find it elsewhere.

This is separate from politics that might impact the researchers themselves, their ability to get and keep a group, ... Problems in this area merely make things worse.

Good. The current way of doing things is entrenched with systemic bloat, and actually discourages innovation. People who are leaving now will create opportunities to explore where that bloat exists, remove it, and figure out how to create new models of R&D. Fingers crossed.