Final answer:
The election of 1864 empowered President Lincoln to more aggressively pursue the political antislavery agenda, as well as a total war campaign, ultimately affecting both the Civil War's course and the nation's political direction.
Step-by-step explanation:
The presidential election of 1864 had significant political and military ramifications during the Civil War, impacting both the trajectory of the war and the nation's political landscape. One of these ramifications is captured in the notion that the election empowered President Abraham Lincoln to more assertively pursue his anti-slavery objectives as well as his aggressive military campaign against the Confederacy. This reflects a broader strategy Lincoln had adopted, which involved the military necessity of weakening the Confederacy by stripping it of slave labor, thereby crippling their war efforts; this approach also included enlisting African Americans into the Union army. Furthermore, by taking such a stance on slavery, Lincoln made it diplomatically challenging for Britain to recognize the Confederacy, thus reinforcing the Union's cause.
The election confirmed Lincoln's mandate to enact his political and military strategies, including the Emancipation Proclamation and the Union's push towards total war. Through these actions, Lincoln further demonstrated his resolve in preserving the Union and ending slavery. As such, the best description of how the election of 1864 had both political and military ramifications would be that it empowered Lincoln to aggressively pursue his political antislavery agenda and his comprehensive military campaign throughout the South (Option C).