So is Wisconsin the key state this election cycle?
I don't see Wisconsin as the key state but it may settle things if (1) Trump and Biden split Pennsylvania and Ohio and (2) they also split Arizona and Michigan.
I'm basing that on the premise that Biden retains the states Hillary captured in 2016 and so there are 38 electoral votes Biden needs to flip if he's to win.
Key States: Pennsylvania (20), Ohio (18). These 2 alone could provide Biden with the 38.
Secondary states: Arizona (11), Michigan (16), Wisconsin(10).