Final answer:
Stephen A. Douglas promoted the Freeport Doctrine, which maintained that territories could decide the slavery issue through local laws, and he opposed the pro-slavery Lecompton Constitution, aligning with his principle of popular sovereignty. The correct answer is option a) and c).
Step-by-step explanation:
Senator Stephen A. Douglas is historically known for promoting the Freeport Doctrine, which he articulated during his debates with Abraham Lincoln. According to this doctrine, Douglas believed that despite the Supreme Court's decision on the Dred Scott case, the residents of a territory had the power to decide whether to allow slavery within their borders using local laws or 'police regulations'. This stance was intended to uphold the principle of popular sovereignty. However, this position antagonized Southern Democrats who supported the expansion of slavery and caused a major rift within the Democratic Party. It is essential to recognize that Douglas also opposed the Lecompton Constitution, which aimed to admit Kansas as a slave state without proper consent from the Free Soilers, showcasing Douglas's commitment to popular sovereignty and his willingness to collaborate with Republicans to defeat this pro-slavery constitution.