4), opposition to polygamy., i.e., Mormons?
Brigham Young began agitating for statehood for ‘Deseret’ right after Mexico ceded the area after the Mexican War in 1848. Sen Stephen A. Douglas (of Lincoln debate fame) represented Mormon interests.
1852, Utah Territory, Federal Territorial officials were in constant conflict with the Mormon’s parallel government and polygamy was part of it. There were grumblings that the Mormons were in rebellion.
Democrats had been advocating popular sovereignty/state’s rights in the long running argument over whether slavery could expand into the territories.
Republicans, advocating a powerful centralized government, in 1856 argued that popular sovereignty was protecting polygamy. This proved to be a potent political weapon.
Buchanan, taking office in 1857, sent an Army detachment to support his new Territorial governor and enforce the laws. The Mormons feared attack and prepared for war. The country was blundering into the Utah War.
There was opposition in Congress to Buchanan sending troops against the Mormons, ironically including from a Pennsylvania Senator who would four years later become Lincoln’s Secretary of War.
The Utah War/Mormon War eventually petered out into a negotiated settlement with little bloodshed. So little most people have never heard of it. But the arguments used by the sides involved makes for eerie reading knowing that the next President would use rationale similar to Buchanan and would hurl us into a war that still echos today.