Who ran for state senate against stephen douglas and had a series of debates about slavery

(As a note, the race was not for State Senate but was instead for the US Senate.)

Abraham Lincoln ran against Stephen Douglas in 1858 for the United States Senate.

Lincoln, a Republican, was running against Douglas, a Democrat. Both were powerful orators and used debates during the campaign to lay out competing visions for the United States.

Douglas won but Lincoln would go on to win the Presidency just a few years later.