My theory is that they want to go down swinging but hope that, unlike Trump, they’ll still be in politics. They trust that the systems of justice and or politics will kill Trump’s political future, leaving his base without a leader.
It’s like the story about the two guys camping who see a bear approaching them. One ties on his running shoes. The other says “Why are you doing that? You can’t outrun a bear.” The guy in the running shoes says “Yes, but I only have to outrun you.”
If Cruz is seen as the Saint Peter to Trump’s Jesus, then he gets to decide how the church works. That’s all this is: a cynical power grab. Whenever these men do anything, that is always the motive. Every time.