The early leader for the Democratic nomination was former President Martin Van Buren, but his rejection of Texas annexation damaged his candidacy. Opposition from former President Andrew Jackson and most Southern delegations, plus a nomination rule change likely specifically aimed to block him, prevented Van Buren from winning the necessary two-thirds vote of delegates to the 1844 Democratic National Convention. The convention instead chose James K. Polk, former Governor of Tennessee and U. S. House Speaker, who emerged as the first dark horse nominee. Polk ran on a platform embracing popular commitment to expansion, often referred to as Manifest Destiny. Tyler dropped out of the race and endorsed Polk. The Whigs nominated Henry Clay, a famous, long-time party leader who was the early favorite but who conspicuously waffled on Texas annexation. Though a Southerner from Kentucky and a slave owner, Clay chose to focus on the risks of annexation while claiming not to oppose it personally. His awkward, repeated attempts to adjust and finesse his position on Texas confused and alienated voters, contrasting negatively with Polk's consistent clarity.