> the law of this land is based on the Constitution, which gives the Supreme Court ultimate authority to interpret the law

The Constitution vests "the judicial Power of the United States" in "one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish" [1].

That isn't the same as "ultimate authority to interpret the law." In practice, SCOTUS does usually have this power, due to Marbury and other precedent. In practice, too, it can be bullied, e.g. by FDR and potentially right now.

[1] https://constitution.congress.gov/constitution/article-3/