Final answer:
The Illinois Senate race in 1858 established Abraham Lincoln as a key national Republican figure and set the stage for his future presidency, despite his loss to Stephen Douglas.
Step-by-step explanation:
The Illinois Senate race in 1858 is significant for firmly establishing Abraham Lincoln as a leading national Republican figure, despite his loss to Stephen Douglas. The highly publicized Lincoln-Douglas Debates allowed Lincoln to bring his stance on slavery to a larger audience and set the stage for his eventual presidential campaign.
The debates highlighted the escalating tensions surrounding the issue of slavery and proved pivotal for Lincoln's political career, as they increased his national visibility and paved the way for the Republican Party's rise in the North.