Dallas supported Van Buren 's bid for another term in the 1844 presidential election , but James K. Polk won the party 's presidential nomination . The 1844 Democratic National Convention nominated Dallas as Polk 's running mate , and Polk and Dallas defeated the Whig ticket in the general election . A supporter of expansion and popular sovereignty , Dallas called for the annexation of all of Mexico during the Mexican – American War . He sought to position himself for contention in the 1848 presidential election , but his vote to lower the tariff destroyed his base of support in his home state . Dallas served as the ambassador to Britain from 1856 to 1861 before retiring from public office
1844 Democratic National Convention
1844 Democratic National Convention
George M. Dallas