The military and government officials can avoid use of the apps, without banning them for Americans. As they have before WeChat, and before the Internet.
I think the notion that WeChat is a threat to national security is honestly ridiculous. National security is a legal excuse to do things Trump otherwise wouldn’t be able to do in his pursuit of a trade war.
There's no way to predict in advance who's going to become a government official. When they do, and if they used WeChat before then, the damage is done. Material on those close to the officials can also be used against them in similar manner.
Again, not condoning the restriction of personal freedoms, but the national security angle is not totally without merit.
I think the notion that WeChat is a threat to national security is honestly ridiculous. National security is a legal excuse to do things Trump otherwise wouldn’t be able to do in his pursuit of a trade war.