I work for a big national lab and I can make a few observations:
a) Postdocs that have already accepted a job are having second thoughts. Statistically speaking, the likelihood of being detained by the ICE with a valid visa is probably about the same as the airplane suffering a catastrophic issue, but for human perception this does not matter. US is just not attractive any more. Nobody wants to enter a country where you are looked up with suspicion. The fact that the salary just dropped 10% in EUR is also not promising.
b) You would be shocked just how much US research institutions rely on foreigners. It seems immigrants support both ends of the economic chain: slaughterhouses and agri jobs on one end and high tech jobs at the other with natives filling in the middle. There are grants for which you need to be a citizen and they are so much easier to get simply because there are so few of them.
c) The mood is totally depressed. We had cuts this year despite CR with draconiam further cuts next year. And I'm talking about physics, not sociology of woke people. Everybody is sniffing for an exit.