Perhaps a Wisconsin FReeper could shine some light on this election if they know any details of it. Obviously this is an odd time of year in the dead of winter, and obviously the left is very motivated to vote - that may have played a roll, but we can not overlook the fact that this is a reliably Republican seat in a district Trump won. I posted an article about them flipping a deep red Oklahoma district a few months back. They've flipped 34 districts. That's nothing to sneeze at. We need to keep this in mind.
I posted an article the other day I wrote regarding some who voted for Trump but said they regretted it after his sh*thole comments. Now obviously that was only a few voters, but things like that aren't good story lines for the Republicans obviously. I know multiple people came out and denied it, but that was later, and the media had gained full control of the narrative. I think the White House could have averted a great deal of controversy with a good statement that night or early the next morning.
While the controversies often seem to cost him about 5 points in the polls, good news tends to build his poll numbers. What if Trump did a road tour to force the media to cover the economy (suggested by Dana Perino as well)? What if he went to swing states and gave speeches promoting his tax bill and had business owners or workers who benefited from it speak? He could have Congressmen/women and Senators from those swing states/districts with him. The media won't show the positive otherwise. Force them to cover it.
Also, the Democrats are saying we can't secure our border unless we give citizenship or status to those here illegally. Trump could do a trip to the border, to swing districts/states and lay out his platform, present the crime statistics and cost of illegal immigration, present his policies, and ask why the Democrats won't secure the borders and protect Americans without amnesty.
Pastor Darrell Scott who worked on Trump's campaign has said that he has worked with Trump on putting together and urban revitalization plan and prison reform. If they get that into gear, that will be good too.
These are a few issues I think he could utilize to motivate voters. Right now, the left is motivating their people by painting Trump as a racist, Hitler, Russian, etc. They aren't running on policy. We have to have good candidates who run on policy. We want people who support the President fully, but perhaps there are districts we will have to settle for a moderate because that's all that can win. Someone who will vote with the President most of the time and confirm judges is better than nothing.