Summary
US immigration officers denied entry to a French scientist traveling to Houston after finding phone messages criticizing the Trump administration.
French research minister Philippe Baptiste condemned the decision, stressing the importance of academic freedom.
US authorities reportedly accused the scientist of “hateful and conspiratorial messages” but later dropped charges.
Baptiste has been vocal against Trump and Elon Musk for cutting research funding and invited American scientists to relocate to France.
I lack credible sources but I assume in a similar case they just let you in and observe every move you make to make sure you don’t overreach the scope of your visit.
Now if you are known public speaker on democracy and are scheduled to speak at universities you may have more trouble but i imagine in this case you either never go there to begin with or at least carry a dummy phone for the time of your travel.