When will Trump finally cave in and re open the government?

Im not sure he will. He has to prove to his base that he's all in. It has nothing to do with security as he is jeopardizing that same security by continuing the shutdown.
Imo he feels he needs reelection. His office is buffering him from legal issues. If he caves on the wall, he likely loses confidence from his base. If nothing else, he is keeping eyes off all the investigations aimed directly at him....