Wisconsin is under one-party rule and it will remain that way under the current gerrymandered legislative districts.
There are many districts now where it is pointless for the dems to put up a candidate. It is like leading a lamb to slaughter.
Instead the Democratic Party should perhaps think about taking the fight to the Republicans on their own turf and run primary candidates, listing themselves as Republicans and abandoning the inter-party contest altogether. The ersatz candidate would not need to hide his or her party background. They would need however to have a populist message (minimum wage, voting rights, the environment,school funding) that would appeal to the independent voters. The dems could organize their base and with some luck, and a low-turnout election, the crossover dems and low-information Republican voters could deliver the goods.
This is not a new strategy and has been tried before. There have been cases where Republicans have recruited a placeholder candidate, a second candidate who would then split the vote of the Trojan Horse candidate and ensure a victory for the incumbent. This can be defeated by not filing until the last minute.
Sure this sounds fanciful but Democrats have to realize that the normal rules of politics no longer apply. So let's use their rules against them.