If that is the case then the Supreme Court is not constrained by the Constitution. That is, the Court could decide a case that directly gives aid and comfort to the enemies of the United States (like, say, forbidding the States to uphold federal immigration law) and nothing can be done about it.
Indeed, if the Constitution is whatever the majority of Justices say it is, then they are a super-legislature and can make whatever laws they please (like Obamacare) and unmake legitimate laws enacted by the states (like what Roe v. Wade did to the states) regardless of any constraint.