Abraham Lincoln became a nationally known political figure based on a series of public debates with Stephen Douglas.
his victory over Douglas for a Senate seat.
his retirement from the House of Representatives.
his support of popular sovereignty.

A). A series of public debates with Stephen Douglas

Explanation:

As per the question, the key cause of Lincoln's nationwide political popularity was 'a sequence of his public debates with the former Democratic senator, Stephen A. Douglas.' The series of seven debates with him regarding the concern over extension of slavery as Douglas had the belief that slavery will automatically come to an end as the product of sovereignty while Lincoln was in favor of a proper law for the abolishment of slavery to outcast it legally. However, the debates could not reach a conclusion yet this point of view made Lincoln extremely popular among the masses.

frederick william of brandenburg-prussia trained his son, frederick, to be a hardy soldier. but frederick disliked rifle shooting and horseback riding. unlike his father, he was interested in french literature. he enjoyed poetry and music and, like some others of the enlightenment, he scoffed at religion. his father thought him soft, frivolous and unmindful of his duties. and when frederick refused to put his signature on a right to succession, for a few moments his father strangled him.

what are you options