Donald Trump's slam of John McCain, in which he called him "not a war hero" because he was "captured," brought condemnation from many of his 2016 rivals--with two notable exceptions.

Ted Cruz and Ben Carson have both declined to bash Trump, without going so far as to explicitly back his comments.

Cruz--who has lavished praise on Trump in the past--told reporters McCain is his "friend," but insisted he would not be participating in "Republican-on-Republican violence."

"I'm not going to go into the gutter with personal attacks," he told Bloomberg.

"You know I recognize that folks in the press love to see Republican-on-Republican violence, and so you want me to say something bad about Donald Trump, or bad about John McCain or bad about anyone else," he said.  "I'm not going to do it."

Carson, meanwhile, chose to take a semi-neutral stance on McCain's heroism. "It depends on your definition of a war hero," he said.

"I think he has done some wonderful things, certainly history is consistent with what we would consider a war hero," he continued. "Do we take that away from him because some people disagree with him politically? I think that's probably stupid."

Watch Cruz's interview below, via Bloomberg: