Another step in limiting free speech and limit international travel. The EU might start to require visas for USA citizens. Currently it is not required for stays shorter than 90 days in a 180 day period (if I am not mistaken).
There's no point in retaliating, since the US is machine-gunning itself in the feet here. European universities are more than happy to invite the world's best and brightest to study there instead.
I guess the irony of scanning social media posts for 'un-American' content is entirely lost here. Still, information control is essential for public order and national security.