Polk's Whig opponent was Henry Clay of Kentucky. (Incumbent Whig President [[John Tyler]]—a former Democrat—had become estranged from the Whigs and was not nominated for a second term.) The question of the annexation of Texas dominated the campaign. Polk was a strong proponent of immediate annexation, while Clay seemed more equivocal and vacillating.
Another campaign issue, also relating to westward expansion, involved the [[Oregon Country]], then under the joint occupation of the United States and [[Great Britain]]. The Democrats had championed the cause of expansion, informally linking the controversial Texas annexation issue with a claim to the entire Oregon Country, thus appealing to both Northern and Southern expansionists. (The slogan "[[Fifty-Four Forty or Fight!]]", often incorrectly attributed to the 1844 election, did not appear until later.) Polk's consistent support for westward expansion—what Democrats would later call "[[Manifest Destiny]]"—likely played an important role in his victory, as it united all the Democratic factions.
In the election, Polk won in the South and West, while Clay drew support in the Northeast. Polk lost his home state of Tennessee but won the crucial state of New York (with the support of many Van Buren supporters, since it was his home state), where Clay lost supporters to the third-party candidate [[James G. Birney]] of the Liberty Party, who was anti-slavery. Also contributing to Polk's victory was the support of new immigrant voters, mostly Irish and German Catholic, who were angered at the Whigs' nativism. Polk won the popular vote by a margin of about 38,000 out of 2.6 million, and took the Electoral College with 170 votes to Clay's 105. Polk won 15 states, while Clay won 11.