The correct answer is "An antislavery coalition in government".
The Great Debate was a series of debates held between Republican candidate Abraham Lincoln and Democratic candidate Stephen Douglas for the position of the senator of the state of Illinois. A debate was held in the 9 congressional districts of Illinois, as at that time the senator was elected by state legislatures.
The main issue of the debates was slavery, as Lincoln was in favor of abolitionism and Douglas strongly opposed it, as he believed slaves were a key element in the South's economy. Therefore, an antislavery coalition in government was not an option.
