Sanders said she was "not going to get into the back and forth on this," in reference to a public apology on the McCain comment.
Cooper rattled off a list of times Trump has demanded apologies from his critics and juxtaposed it with one single apology issued by the president.
The political pundit said McCain was making his life count.
California Representative Duncan Hunter's candor came after a week of Trump surrogates hurling insults at McCain, whose announcement that he would be opposing CIA pick Gina Haspel roiled some within his own party.
"I don't understand what kind of environment you're working in when that would be acceptable and then you could come to work the next day and still have a job," Meghan McCain said.
"It doesn't matter, he's dying anyway," Kelly Sadler said during an internal meeting.
The senator's comments were "just insensitive and again, it's not appreciated at this moment."
John McCain is fighting a brain tumor.
The pair have a long-running feud.