The time to do this would've been immediately after it was discovered that Trump took classified documents and had them in his home during visits from foreign agents.

The Republicans would've howled about it, but I think it could have been done, at that moment. Like, have the first news about it not be talking about the documents, but simply that former President Trump has been detained and will not be allowed to communicate with anyone but his legal representation, because of suspicion of potential coded communication to enemy agents.