This study explores the Republican Party's origins at the institutional level, specifically in the 34th House of Representatives. We focus on an especially critical event, the House speakership election of 1855-56, which resulted in the first major victory for the new party. We conduct our analysis by applying the spatial theory of voting to the House balloting for Speaker, using a scaling technique developed by Poole (1998). Results from our spatial model suggest that slavery was the overriding determinant of vote choice throughout the two-month speakership battle. Its effects were considerable from the outset, even in multiple candidate rounds, and proved to be more influential as the balloting progressed. We also find that the issue of nativism, which was so important in the previous congressional elections and would continue to affect the Republicans' electoral fortunes for several more years, had no impact on members' votes for speaker. Once elected, the new Republican speaker, Nathaniel Banks organized the House around anti-slavery tenets, stacking both committees and chairs with anti-slavery advocates. Overall, these results suggest that while the Republicans would struggle for an electoral identity deep into the 1850s - balancing the competing interests of slavery and nativism to win office - they emerged as a single-issue, anti-slavery coalition at the institutional level as early as 1855.