Well what Cruz does himself is certainly on him, but we can’t hold him responsible for those claiming to be his fans.
Some are zealots who are clueless about the damage that they are doing to Cruz, all sides have some of those, but some of the most strident may be agents provocateurs who are killing two birds with the same stone, Trump and Cruz.
Or for Hillary, or just trying to cause general dissension in the ranks.
My point is it’s hard to finger Cruz “supporters” as shills when Cruz himself has become unhinged. It’s just as likely they mean it.