I don’t know how anyone could disagree with Kagan here in good faith. Of course congress has the power to regulate the supreme court. They’ve passed numerous regulations for the court in the past, and the constitution expressly gives the power to regulate the specifics of the court to congress. Even the number of justices in the court is chosen by congress. It wasn’t nine until they passed a bill saying it was. And congress can impeach and remove justices too. I think the more corrupt members of the court just fear any actual oversight happening for once.