Final answer:
President Polk asked Congress to declare war on Mexico.
Step-by-step explanation:
When President Polk heard that fighting had occurred on the Mexico border, he asked the Congress to declare war on Mexico. Polk believed that Mexico had invaded U.S. territory and shed American blood on American soil, which led to his demand for war. Despite opposition from some members of the Whig party, Congress overwhelmingly approved the declaration of war. This eventually led to the Mexican-American War, which lasted from 1846 to 1848.