due to the fear of stoking the debate over slavery. Tyler was nonetheless determined to pursue annexation because he believed that the British conspired to abolish slavery in Texas and because he saw the issue as a means to reelection, either through the Democratic Party or through a new party. In April 1844, Secretary of State John C. Calhoun reached a treaty with Texas providing for the annexation of that country. Clay and Van Buren, the two front-runners for major-party presidential nominations in the 1844 election, both announced their opposition to annexation, and the Senate blocked the annexation treaty. To the surprise of Clay and other Whigs, the 1844 Democratic National Convention rejected Van Buren in favor of James K. Polk and established a platform calling for the acquisition of both Texas and Oregon Country. Having won the presidential nomination at the 1844 Whig National Convention unopposed, Clay and other Whigs were initially confident that they would defeat the divided Democrats and their relatively obscure candidate. However, Southern voters responded to Polk's calls for annexation, while in the North, Democrats benefited from the growing animosity towards the Whig Party among Catholic and foreign-born voters. Ultimately, Polk won the election, taking 49.5% of the popular vote and a majority of the electoral vote; the swing of just over one percent of the vote in New York would have given Clay the victory. Polk and the Mexican–American War, 1845–1849 In the final weeks of Tyler's presidency, a small group of Southern Whigs joined with congressional Democrats to pass a joint resolution providing for the annexation of Texas, and Texas subsequently became a state in 1845. Following the annexation of Texas, Polk began preparations for a potential war with Mexico, which still regarded Texas as a part of its republic and contended that Texas's true southern border was the Nueces River rather than the Rio Grande. After a skirmish known as the Thornton Affair broke out on the northern side of the Rio Grande, Polk called on Congress to declare war against Mexico, arguing that Mexico had invaded American territory by crossing the Rio Grande. Many Whigs argued that Polk had provoked war with Mexico by sending a force under General Zachary Taylor to the Rio Grande, but only a minority of Whigs voted against the declaration of war as they feared that opposing the war would be politically unpopular. Polk received the