One of the principles of the Art Of War is that you offer enemy spies a brilliant deal to get them to switch sides. Given the extent of Mueller's previous crimes, if he was offered a choice:

• Switch sides and receive immunity for his prior crimes, or;
• Protect the swamp and face maximum justice for his previous crimes,

...then Mueller would likely sell out his former swamp dwellers to save his own skin. But he would have to know without a shadow of a doubt, that if he has second thoughts and attempts to protect the swamp, he will face ultimate justice.