Research indicates that polarization has led to an increasing dispersion between moderate and more extreme voters within both parties. Intraparty polarization supposedly affects the nature of interparty competition as it creates political space for new political realignments and the rise of anti-establishment candidates. This article examines the extent and impact of intraparty polarization in Congress on US trade policy. Specifically, the article examines whether (and which) trade policy preferences are distributed within and between both parties, as well as how intraparty polarization has influenced the outcome of US trade negotiations. It is theorized that intraparty polarization causes crosscutting legislative coalitions around specific trade policies and political realignments around ideological factions, with consequences for the outcome of trade negotiations. By relying on a unique dataset of congressional letters and co-sponsorship legislation, the article first derives trade policy preferences from members of Congress and computes their ideological means. Two contemporary cases of US trade policy are examined: The Transpacific Partnership Agreement and the US–Mexico–Canada Agreement. Via a structured-focused comparison of both cases, the paper finally assesses under which combinations of preference-based and ideology-based intraparty polarization Congress manages to ratify trade agreements. Findings suggest that both parties are intrinsically polarized between free trade and fair trade preferences yet show variance in their degree of ideology-based intraparty polarization. These findings contribute to existing work on bipartisanship as well as factions in the foreign policy realm, as it shows under which circumstances legislators can build crosscutting coalitions around foreign policies.

研究表明，两极分化导致两党内温和选民和更极端选民之间的分歧越来越大。党内两极分化据称会影响党际竞争的性质，因为它为新的政治调整和反建制候选人的崛起创造了政治空间。本文考察了国会党内两极分化对美国贸易政策的程度和影响。具体而言，本文考察了双方内部和之间是否（以及哪些）贸易政策偏好分布，以及党内两极分化如何影响美国贸易谈判的结果。从理论上讲，党内两极分化导致围绕特定贸易政策的跨领域立法联盟和围绕意识形态派别的政治调整，对贸易谈判结果的影响。通过依赖国会信件和共同提案立法的独特数据集，文章首先从国会议员那里推导出贸易政策偏好并计算他们的意识形态手段。研究了美国贸易政策的两个当代案例：跨太平洋伙伴关系协定和美国-墨西哥-加拿大协定。通过对两种情况进行结构化的重点比较，本文最终评估了基于偏好和基于意识形态的党内两极分化国会在哪些组合下设法批准贸易协定。研究结果表明，双方在自由贸易和公平贸易优惠之间本质上是两极分化的，但在基于意识形态的党内两极分化程度方面表现出差异。