Miami Rebel is absolutely right.
There's plenty of easily found video of Trump on the phone with Walz, praising what a great job he's doing while Minneapolis burned.
How can Trump criticize him now? "You said personally I was doing a great job!"
Why did Trump tell Walz he was doing a great job when clearly he wasn't is the real question.
Pretty much for the same reason that Hulk Hogan was a headliner at the RNC convention. As has been said of Trump, "he's a weak man's vision of a strong man."
Trump (and many of his most rabid fans) are smooth-brained types who are suckers for the image of what they perceive as "strength," that's all. But, hey, that's where the country is nowadays: two completely synthetic people competing for the Presidency.