It strikes me as intuitively powerful that an interest under state law that is sufficient to enable a party to intervene as of right as a defendant in a federal case is also sufficient to enable that defendant to pursue an appeal of a ruling that is adverse to that interest.
As I read it, the case that Judge Walker invokes to call into question Prop 8 proponents’ standing to appeal—Arizonans for Official English v. Arizona (1997)—supports the principle that a party’s standing to defend a ballot proposition in federal district court is co-extensive with that party’s standing to appeal an adverse decision on that ballot proposition. In that case, the Court stated that “Standing to sue or defend is an aspect of the case or controversy requirement” and that it was “aware of no Arizona law appointing initiative sponsors as agents of the people of Arizona to defend, in lieu of public officials, the constitutionality of initiatives made law of the State.” (Emphasis added.) It was on that basis that the Court expressed its “grave doubts” whether the initiative sponsors had “standing under Article III to pursue appellate review.”
Conversely, if Prop 8 proponents don’t have standing to appeal Walker’s ruling, then it ought to follow that they also had no authority to intervene as of right as defendants to defend Prop 8. And, given the state defendants’ refusal to defend Prop 8, that would mean that there were no proper parties who were genuinely adverse to plaintiffs. It may well be (though the question, I acknowledge, presents complications) that, under the Supreme Court’s ruling in Moore v. Charlotte-Mecklenburg Board of Education (1971), the case would therefore have lacked the requisite adverseness to satisfy the “case or controversy” requirement under Article III of the Constitution—and that Judge Walker would have been obligated to dismiss plaintiffs’ case (rather than proceed to judgment on the merits). (In the Arizonans case, the governor defended the case in the district court, but then chose not to appeal, so any doubts about the standing of the initiative sponsors to pursue an appeal wouldn’t affect the existence of a “case or controversy” in the district court.)
(Thanks to Hashim Mooppan of Jones Day for calling Moore to my attention.)