Congress could always pass a law saying "the Supreme Court can not rule on the constitutionality of this", like they did with Medicare.
Congress does not have the constitutional authority to ban SCOTUS from reviewing a law. The Supreme Court's power of review comes from the constitution, not Congressional mandate; that power wasn't something granted by Congress so Congress can't just take it away. Nothing in the constitution even arguably gives Congress the right to make itself immune to the other branches.
False.
https://en.wikipedia.org/wiki/Jurisdiction_stripping
Wait, this has been a thing this whole time!? Why isn't this used more often?
Also, could Congress enact a requirement by statute that, for example, the Supreme Court can only strike down a law passed by an elected legislature by a margin of 6-3 or greater?
It's not used because everyone involved knows that if the Court wanted to strike down a particular law from which its jurisdiction were stripped, it would find the relevant jurisdiction-stripping provision unconstitutional, too, rendering the whole exercise pointless. There are a lot of writings out there about how jurisdiction-stripping could be unconstitutional. It's not exactly written in the text of the Constitution, but, frankly, neither is judicial review to begin with.
