MANHATTAN, Kan. (AP) — Republican Sen. Pat Roberts, the longest-serving member of Congress in Kansas history, announced Friday that he won't run again in 2020, setting up a scramble to replace him in a GOP-leaning state where Democrats are energized by key victories in last year's midterm elections.

The 82-year-old, four-term senator was likely to have faced grueling primary and general election contests next year, just as he did in 2014 when his longevity on Capitol Hill became a political liability for him.

Democrats haven't won a Senate seat in Kansas since 1932. However, Democrat Laura Kel...