Contemporary protectionist policies in the U.S. are often initiated by the executive branch but enforced unevenly across firms. We argue that such uneven enforcement arises because legislators—with both institutional capacity and local motivation—shield connected firms from executive protectionist measures. We test this claim using the Trump administration’s Buy American Act (BAA), which penalized firms reliant on foreign, especially Chinese, suppliers. Combining firm-level data on federal contracts, supply chains, and campaign contributions, we analyze 1,958 firms (2015–2019). A difference-in-differences design shows that the BAA significantly reduced contracts for firms with Chinese suppliers, but only among politically inactive firms in districts represented by less powerful House members or by members lacking strong local ties. We also find that only less-connected firms adjusted their suppliers after the BAA. These findings highlight the importance of distinguishing between the adoption and implementation of protectionist policies, and how legislators shape implementation amidst presidential dominance in trade policy.