of new voters in the North and the collapse of Whig strength in much of the South. Collapse, 1853–1856 Despite their decisive loss in the 1852 elections, most Whig leaders believed the party could recover during the Pierce presidency in much the same way that it had recovered under President Polk. However, the strong economy still prevented the Whig economic program from regaining salience, and the party failed to develop an effective platform on which to campaign. The debate over the 1854 Kansas–Nebraska Act, which effectively repealed the Missouri Compromise by allowing slavery in territories north of the 36°30′ parallel, shook up traditional partisan alignments. Across the Northern states, opposition to the Kansas–Nebraska Act gave rise to anti-Nebraska coalitions consisting of Democrats focused on this opposition along with Free Soilers and Whigs. In Michigan and Wisconsin, these two coalitions labeled themselves as the Republican Party, but similar groups in other states initially took on different names. Like their Free Soil predecessors, Republican leaders generally did not call for the abolition of slavery but instead sought to prevent the extension of slavery into the territories. Another political coalition appeared in the form of the nativist and anti-Catholic Know Nothing movement, which eventually organized itself into the American Party. Both the Republican Party and the Know-Nothings portrayed themselves as the natural Whig heirs in the battle against Democratic executive tyranny, but the Republicans focused on the "Slave Power" and the Know-Nothings focused on the supposed danger of mass immigration and a Catholic conspiracy. While the Republican Party almost exclusively appealed to Northerners, the Know-Nothings gathered many adherents in both the North and South; some individuals joined both groups even while they remained part of the Whig Party or the Democratic Party. Congressional Democrats suffered huge losses in the mid-term elections of 1854, as voters provided support to a wide array of new parties opposed to the Democratic Party. Though several successful congressional candidates had campaigned only as Whigs, most congressional candidates who were not affiliated with the Democratic Party had campaigned either independently of the Whig Party or in collusion with another party. As cooperation between Northern and Southern Whigs increasingly appeared to be impossible, leaders from both sections continued to abandon the party. Though he did not share the nativist views of the Know-Nothings, in 1855 Fillmore became a member of the Know-Nothing movement and encouraged his Whig followers to join