Senator Robert J. Walker of Mississippi, a close Polk ally, suggested former senator George M. Dallas of Pennsylvania. Dallas was acceptable enough to all factions and gained the vice-presidential nomination on the next ballot. The delegates passed a platform and adjourned on May 30.[90][91]
Although many contemporary politicians, including Pillow and Bancroft, claimed the credit in the years to come for getting Polk the nomination, Walter R. Borneman felt that most of the credit was due to Jackson and Polk, "the two who had done the most were back in Tennessee, one an aging icon ensconced at the Hermitage and the other a shrewd lifelong politician waiting expectantly in Columbia".[92] Whigs mocked Polk with the chant "Who is James K. Polk?", affecting never to have heard of him.[93] Though he had experience as Speaker of the House and Governor of Tennessee, all previous presidents had served as vice president, Secretary of State, or as a high-ranking general. Polk has been described as the first "dark horse" presidential nominee, although his nomination was less of a surprise than that of future nominees such as Franklin Pierce or Warren G. Harding.