There are only 45 people who can walk into the justices’ offices, including the nine supremes.
One of them will become a hero of the Left.
Any clerk is a possibility. I went to college with a fellow who wound up clerking for both Brennan and Souter. Just because someone would take a prestigious assignment with Roberts or Gorsuch, doesn’t mean he’s any more conservative than a typical National Review writer.
There are approximately 250 SCOTUS employees, including administrative and clerical people. If draft decisions and related materials can be accessed by admin and clerical individuals, that expands the universe of possible leakers to greater than 45 although none of us outside the court can know the exact number.
We also don't know the procedures under which those materials are kept. Are they highly secured both in paper form and electronically? Or is security around them relatively lax because...well, because of attitudes like "it's the Supreme Court and who would do such a thing."