Trump has decided that Waltz is too much trouble
in his current 'security' role - but doesn't hate
him. As such, Waltz is moving over to be UN ambassador
(someone remarked it meant a VERY nice apartment)
and an unnamed Someone Else will be found to be
Security Advisor.
PART of this is the "Signal" thing - but I suspect
there were other problems too.
Hey, sometimes you just have to TRY someone at a
job and eval afterwards. MAYbe they'll rise to the
challenge, MAYbe not.