Van Buren easily won renomination for a second term at the 1840 Democratic National Convention, but he and his party faced a difficult election in 1840. Van Buren's presidency had been a difficult affair, with the U.S. economy mired in a severe downturn, and other divisive issues, such as slavery, western expansion, and tensions with Great Britain, providing opportunities for Van Buren's political opponents—including some of his fellow Democrats—to criticize his actions. Although Van Buren's renomination was never in doubt, Democratic strategists began to question the wisdom of keeping Johnson on the ticket. Even former president Jackson conceded that Johnson was a liability and insisted on former House Speaker James K. Polk of Tennessee as Van Buren's new running mate. Van Buren was reluctant to drop Johnson, who was popular with workers and radicals in the North and added military experience to the ticket, which might prove important against likely Whig nominee William Henry Harrison. Rather than re-nominating Johnson, the Democratic convention decided to allow state Democratic Party leaders to select the vice-presidential candidates for their states.