What Kushner did disassembled something like 30 years of UN effort in the region. He enabled an alliance between two bullies who could agree on a couple of things, and will now use that alliance to beat the shit out of people that disagree with them, to the detriment of, say Palestine.

This "accomplishment" is the equivalent to smuggling some dinosaur embryos to a south american island in a cryogenic cylinder disguised as shaving cream. It's not so much that career diplomats COULDN'T do it, it's that they understood why they SHOULDN'T do it.