Whose Guarantee Counts? Treaty Cues and U.S. Signals in European Support for Defending Allies

This project studies how treaty cues (NATO Article 5 vs. EU Article 42(7)) and U.S. involvement shape Europeans' willingness to aid an ally under attack. I develop a micro‑founded model where support depends on expected coalition success (a provision-point public good), a deontic sufficiency norm triggered by invoking a clause, and an abandonment penalty when the United States withholds support. The model yields shape predictions: a kink at the action viewed as minimally compliant, a near‑threshold pivotality spike when U.S. support escalates from equipment to troops, and a stronger withholding penalty under NATO. I test these claims in a 3*4 survey experiment across twelve EU countries that orthogonally varies the clause cue and U.S. stance and measures approval for sanctions, equipment, and troop deployments. The project informs debates on strategic autonomy and the transatlantic bargain by linking micro-foundations to experimental evidence. Substantively, this project shed light on whether EU legal commitments can substitute for NATO in mass opinion and thus enable conditional pathways to European capacity‑building.