Considering Trump is using the liberal end of twitter, the internet, and media to basically to try to take out Cruz for him, I sure as hell ain't underestimating him.
Think of it this way, he basically has every dem supporter dreaming (and in turn, perpetuating and spreading to the main stream and online) the idea that Cruz is a serial philanderer; without ever saying anything. He's basically getting Democratic voters & supporters to do his dirty work for him without even trying.
He's flat out playing us like fiddles. That alone terrifies me in a general election.