The 'swinging back' clearly began with the April 2018 Supreme Court election

From 12 blue counties in 2016 to 35 blue counties in 2018.

Headline from Milwaukee Journal Sentinel, 11/1/2018

Related reading:
'Blue Wave Builds' In Wisconsin's Supreme Court Election.  Milwaukee County Judge Rebecca Dallet Won Counties That Have Been Trending Republican For A Decade.  (Wisconsin Public Radio, 4/4/2018)