The problem's not the "ex post facto". The problem is the "Bill of Attainder". You can't pass a law that, e.g., breaks up Amazon - to do so would be to deprive

The problem's not the "ex post facto". The problem is the "Bill of Attainder". You can't pass a law that, e.g., breaks up Amazon - to do so would be to deprive them of property without trial. But you can create a law that Amazon (and potentially others) will be in violation of, and following proper trial, they are broken up.