Caldara v. City of Boulder, 955 F.3d 1175

In May–June 2018 Boulder enacted Ordinance 8245 (amended by 8259), banning sale/possession of defined “assault weapons” and large-capacity magazines and raising firearm possession age to 21.
Plaintiffs (Boulder residents and gun-related businesses/entities) sued in federal court, alleging the ordinance is preempted by Colo. Rev. Stat. §§ 29-11.7-102 & 103 and violates federal and state constitutional rights.
The district court abstained under Pullman and stayed the federal case pending resolution in Colorado state court of whether state law preempts the ordinance; a parallel state-court challenge (Chambers) was already pending.
Plaintiffs appealed the abstention order to the Tenth Circuit, arguing Pullman did not apply and abstention unreasonably delayed adjudication of Second Amendment rights.
The Tenth Circuit held Pullman abstention was appropriate: Colorado law is uncertain as to home-rule preemption, state-court resolution could eliminate or narrow federal constitutional questions, and federal resolution risks intruding on important state policy choices.
The Tenth Circuit affirmed the district court’s stay as a proper, non-abusive exercise of discretion.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether district court should abstain under Pullman	Pullman not satisfied; Colorado precedent (City & Cty. of Denver) provides sufficient clarity; abstention improperly delays Second Amendment relief	Colorado law remains uncertain about home-rule vs. state preemption; state resolution could render constitutional questions unnecessary	Affirmed. Pullman abstention appropriate; district court did not abuse discretion
Whether the three Pullman factors are met (uncertain state law; state interpretation could avoid/limit federal issue; federal error would harm state policies)	Argues first factor fails because prior Colorado decision resolves questions	Points to Colorado Supreme Court’s evenly divided decision and lack of controlling state-law clarity; state resolution could obviate or narrow federal claims	All three Pullman factors satisfied: state law uncertain; state interpretation could remove/substantially narrow constitutional issues; federal decision risks disrupting state policy
Whether abstention unacceptably delays/ chills constitutional rights (esp. Second Amendment)	Abstention chills fundamental right and causes undue delay; federal adjudication necessary	No categorical bar to abstention in rights cases; parties could have sought certification; parallel state-case mitigates delay	Abstention permissible; district court properly balanced delay against federalism and allowed stay; no abuse of discretion

Railroad Comm’n of Texas v. Pullman Co., 312 U.S. 496 (establishing Pullman abstention doctrine to avoid premature constitutional rulings)
City of Chicago v. Fieldcrest Dairies, 316 U.S. 168 (applying Pullman where state courts should resolve statutory/ordinance conflict to avoid federal-state friction)
Babbitt v. United Farm Workers Nat’l Union, 442 U.S. 289 (caution against premature constitutional adjudication)
Moore v. Sims, 442 U.S. 415 (affirming abstention despite constitutional claims in presence of controlling state-court proceedings)
Harman v. Forssenius, 380 U.S. 528 (recognizing district court discretion to abstain and instructing consideration of nature of the constitutional deprivation)
Hill v. City of Houston, 482 U.S. 451 (denying Pullman where state law was clear and municipal practice abundant)
Arizonans for Official English v. Arizona, 520 U.S. 43 (Pullman avoids federal-court error deciding unsettled state-law questions)
Kan. Judicial Review v. Stout, 519 F.3d 1107 (10th Cir. standards for Pullman abstention analysis)
Vinyard v. King, 655 F.2d 1016 (10th Cir.: clarity of state law is a legal question reviewed de novo; district appraisal of policy disruption afforded deference)
City & Cty. of Denver v. State, 788 P.2d 764 (Colo. 1990) (Colorado home-rule/preemption framework discussed and later evenly split by Colorado Supreme Court on related ordinance challenge)