His defense rests without mounting any defense at all.
He is either:
1. Falling on his sword for his Dear Leader,
2. Protecting his family from drinking Russian Polonium tea
3. or has been paid off. (Family gets to live well, while he spends the rest of his life in prison.)
The funny thing is that if it is #1, and Trump pardons him, that opens up Trump to some seriously vicious investigation. It'll make the Mueller investigation look like a Girl Scout cookout.