Challenging a constitutional amendment?

A commenter asks:

I saw something on SFgate.com about the possibility of the California Supreme Court declaring this new amendment unconstitutional if it passes. Is that legally possible in California? Can the state supreme court do that to a new amendment?

This argument has been raised with respect to the proposed constitutional amendments in both California and Massachusetts . There are really two very different arguments suggested here:

1) The state constitution would then violate the federal constitution.

This is pretty straightforward, since the Supremacy Clause says the U.S. Constitution trumps state constitutions. Don't expect to this sort of claim pursued, however; litigating marriage in the conservative-dominated federal courts in the foreseeable future is probably not a wise strategic move for the LGBT equality movement.

2) The new state amendment would be so inconsistent with the existing provisions of the state constitution that it would be invalid.

This theory was floated in a concurring opinion by two Massachusetts high court justices in Schulman v. Attorney General (PDF). In Schulman the court held that the state constitution did not forbid a proposed constitutional amendment that would reverse Goodridge v. Dept. of Public Health and ban same-sex marriages. The court held that, although the constitution forbids amendments designed to "reverse a judicial decision," that provision applies only attempts to reverse the application of law in a particular case, not amendments seeking to change the applicable legal standard.

The court was unanimous on this point, but two justices wrote a concurring opinion that raised the possibility of a different challenge to the amendment if it were enacted. Justice Greaney wrote that:

There is no Massachusetts precedent discussing, or deciding, whether the initiative procedure may be used to add a constitutional provision that purposefully discriminates against an oppressed and disfavored minority of our citizens in direct contravention of the principles of liberty and equality protected by art. 1 of the Massachusetts Declaration of Rights. ... Put more directly, the Goodridge decision may be irreversible because of its holding that no rational basis exists, or can be advanced, to support the definition of marriage proposed by the initiative and the fact that the Goodridge holding has become part of the fabric of the equality and liberty guarantees of our Constitution. If the initiative is approved by the Legislature and ultimately adopted, there will be time enough, if an appropriate lawsuit is brought, for this court to resolve the question whether our Constitution can be home to provisions that are apparently mutually inconsistent and irreconcilable.

This is, as far as I'm aware, a completely novel argument. It has a certain logic to it, and deserve careful thought, but my initial impression is that this theory is not a winner. Democratic constitutions can be amended by the people, even if they reverse the effects of existing provisions. The Reconstruction Amendments, for example, fundamentally altered the relationship between federal and state government, in a way that flew in the face of then-established understandings of federalism and enumerated congressional powers. That was the point!

The difference here is that an amendment would not expand but limit the established rights of individuals as against the government. This is, I think, the distinction Justice Greaney would draw, but I am not sure it is a compelling one. If the California or Massachusetts constitution are amended, we shall see.

(There's a third possible argument under some other state constitutions: that a new amendment is invalid because it is addresses multiple, distinct subjects. But this argument a) has failed in other states so far, b) is as far as I know based on language absent from the CA or MA constitutions, and c) would not apply to the CA ballot measure in any case, because it addresses only marriage and not civil unions, domestic partnerships or anything else.)