Usually when people say stupid or cruel things, they apologize and move on, instead of defiantly standing by their statements. But that doesn't happen in Trumpworld, and it certainly hasn't happened in the case of White House staffer Kelly Sadler's callous remark about John McCain.

The big picture: Once you’ve worked for Trump for a while you know that the worst thing you can do, the biggest show of weakness, is to apologize. He never does and never did (with one exception — the "Access Hollywood" tape). So staff knows that if they publicly apologize they’re actually MORE likely to incur Trump’s wrath than if they just move on.

In this specific case I'm told that White House Press Secretary Sarah Sanders was so furious about the leak that she didn’t want to say anything publicly to validate it. And other White House staffers like Mercedes Schlapp defended Sadler privately because they believed she was being viciously targeted by colleagues.

I asked a senior administration official about the phenomenon this morning. Here's how he explained it:

"Not apologizing is a core operating principle for Trump. The basic belief is that you never actually get ‘credit’ — from the Left, the media, political opponents, etc. — for apologizing, so why do it? Even the Access Hollywood response video included a defiant Trump going after the ‘actions’ of Bill Clinton and ‘bullying of victims’ by Hillary, and ended with ‘See you at the debate!'"