It’s so incredibly obvious they fear that an outsider will uncover the complete scam that is the modern federal government. I think they’re afraid of both Cruz and Trump, but they know Trump would put the hammer down.
They don’t fear Cruz. He is one of them, and a poor one without any power, at that.
The only one they fear is Trump, because he is rich and powerful and has many connections. He’s the one that poses the threat.