Actually a clerk for Justice Ketanji Brown Jackson is the most likely suspect since it happened immediately after she got sworn in and she IS a radical leftist; and therefore she likely also surrounded herself with radical leftist law clerks.
PEOPLE ARE WONDERING WHY THE FBI CAN'T FIND THE SCOTUS MEMO LEAKER. IT'S NOT AS IF THEY HAVE GOT A HUGE POOL OF VIABLE SUSPECTS. BECAUSE IT WAS MOST LIKELY LEAKED BY A DEM PARTY OPERATIVE . . . AND WE DON'T WANT TO EMBARRASS OUR DEM PARTY MASTERS.