The UN headquarters agreement grants immunity to world leaders when travelling to New York for these events

I get what you're saying but I don't think another letter from the UN is going to accomplish anything so that feels like an empty ideal to hold to

It would be politically stupid to violate diplomatic immunity of a guest of the UN when your country doesn't even officially recognise the authority of the ICC. The federal government already doesn't like him; they'd be creaming their pants at the opportunity to get his ass over violating federal and international law. Hell, they'd be obliged to, and every other signatory to the UN that guaranteed this diplomatic immunity would have to back them up.

Besides, it's not like he'd achieve much. Briefly jailing Netanyahu would make him look like a martyr, but it's only a question of time until Trump busts his buddy out of there.

Much as we might love to see it happen, Mamdani has to pick his battles. He can do more good by staying in office than by picking a fight with the world.

And ultimately, isn't Trump shitting on international agreements one of the things sabotaging the US' diplomatic standing?

Exactly.

What about UHC CEO and conservative podcast guy. Somehow the Trump assassination attempts were all failures though. Makes you wonder. Maybe secret service is just that good.

It's a show of intent. He wouldn't have announced it if he thought he could get away with it; he'd just have done it. But by expressing that he'd like to arrest this guy, he signals a political stance that he knows will make him unpopular with a certain influential political activism group.