Many Southerners backed Calhoun's candidacy, Westerners rallied around Senator Lewis Cass of Michigan, and former Vice President Johnson also maintained a strong following among Democrats. Jackson assured Van Buren by letter that Polk in his campaigns for governor had "fought the battle well and fought it alone". Polk hoped to gain Van Buren's support, hinting in a letter that a Van Buren/Polk ticket could carry Tennessee, but found him unconvinced. The biggest political issue in the United States at that time was territorial expansion. The Republic of Texas had successfully revolted against Mexico in 1836. With the republic largely populated by American emigres, those on both sides of the Sabine River border between the U.S. and Texas deemed it inevitable that Texas would join the United States, but this would anger Mexico, which considered Texas a breakaway province, and threatened war if the United States annexed it. Jackson, as president, had recognized Texas independence, but the initial momentum toward annexation had stalled. Britain was seeking to expand her influence in Texas: Britain had abolished slavery, and if Texas did the same, it would provide a western haven for runaways to match one in the North. A Texas not in the United States would also stand in the way of what was deemed America's Manifest Destiny to overspread the continent. Clay was nominated for president by acclamation at the April 1844 Whig National Convention, with New Jersey's Theodore Frelinghuysen his running mate. A Kentucky slaveholder at a time when opponents of Texas annexation argued that it would give slavery more room to spread, Clay sought a nuanced position on the issue. Jackson, who strongly supported a Van Buren/Polk ticket, was delighted when Clay issued a letter for publication in the newspapers opposing Texas annexation, only to be devastated when he learned Van Buren had done the same thing. Van Buren did this because he feared losing his base of support in the Northeast, but his supporters in the old Southwest were stunned at his action. Polk, on the other hand, had written a pro-annexation letter that had been published four days before Van Buren's. Jackson wrote sadly to Van Buren that no candidate who opposed annexation could be elected, and decided Polk was the best person to head the ticket. Jackson met with Polk at the Hermitage on May 13, 1844 and explained to his visitor that only an expansionist from the South or Southwest could be elected—and, in his view, Polk had the best chance.