Kerr v. Hickenlooper, 744 F.3d 1156 (10th Cir. Mar. 7, 2014), reh’g en banc denied, 759 F.3d 1186 (10th Cir. July 22, 2014)- 

”[M]embers of a state legislature may have standing to sue in order to vindicate the ‘plain, direct and adequate interest in maintaining the effectiveness of their votes.’” Id. at 1163 (citation omitted). The Tenth Circuit Court of Appeals held that legislator – plaintiffs have Article III standing to bring suit to enjoin enforcement of an act that could violate the Guarantee Clause of the United States Constitution, withstanding the political question doctrine and challenges to prudential standing. Colorado’s Taxpayer’s Bill of Rights (TABOR) requires referendum approval of most tax increases. State legislators challenged the constitutionality of TABOR. The court only considered the issues of standing and the political question doctrine, avoiding the merits of the case. Article III standing requires that the plaintiff demonstrate (1) a concrete injury, (2) causation, and (3) redressability. The court found that “nullifying a legislator’s vote or depriving a legislator of an opportunity to vote is an injury in fact,” id. at 1166 (citation omitted), that the enforcement of the act is sufficient causation, and that barring enforcement is sufficient redressability. The court distinguished TABOR from situations where a legislator might have been “[s]eeking to obtain a result in a courtroom which he failed to gain in the halls of the legislature.” Id. at 1167 (citation omitted).