President Tyler was a disappointment to the Whigs, and they nominated Senator Henry Clay for president in 1844. The Democrats nominated the “dark horse,” James Polk. He supported the annexation of the Texas Republic. After taking office Polk sent a diplomat to Mexico to offer up to $40 million to pay for land including Texas and California, and to settle a dispute over the Texas border. The Mexican government was willing to discuss the Texas border issue, but did not care to sell its territory outside Texas.
Polk had another issue to settle in the Pacific Northwest. The U.S. and England had shared control of the Oregon Country (which contained the area that is now Washington, Oregon, and Idaho) since 1818. Some westerners wanted the U.S. to have sole possesson to North latitude 54 degrees, 40 minutes, which would have taken half of what is now British Columbia. In the election, Polk supporters chanted the formula “54-40 or fight.”
 Polk took a firm stand by claiming the Oregon Territory for the U.S., and this did not receive a warm reception in England. The U.S. was faced with the threat of fighting wars with both Mexico and Great Britain.
Fortunately, Great Britain and the U.S. had come close to an agreement before, and the U.S.-Canadian boundary through the Oregon Country was determined peaceably, though not on terms the 54-40 crowd had in mind.
On the other hand, the Texas boundary dispute with Mexico led to war. The Mexican War was denounced by Whigs and northern Democrats who claimed Polk was trying to expand the territory open to slave owners.
 Mexican officials might have wondered why war was threatened over a border issue on which they were willing to negotiate. The real motivation, according to the evidence, was to obtain California and the Southwest for the United States. President Polk believed that Mexico could not maintain its grip on California, and better for the U.S. to seize that prize than someone else.