While Southern Whigs cast doubt on his devotion to slavery, his supporters insisted he believed in three things: that Congress could not interfere with slavery in the states, that it would be 'impolitic' to abolish slavery in the District of Columbia, and that agitation about slavery endangered the union. Van Buren and his supporters realized that to build a viable national party and to maintain the union they had to compromise by accepting slavery. The Democrats created the first modern party, but in doing so consciously removed slavery and abolition from the partisan agenda.