Ryan won 65-30 in 2016. Trump also won the district 53-41. I don't think Ryan is going to lose his seat. I can see him just resigning if he loses the speakership which is possible.
Ryan also only won by 10 points in 2012 against a who cares candidate. I can definitely recognize that beating Ryan would mean Democrats have already won the House and then some, but it doesn't hurt that Dems have a credible candidate for once.
Zerban was a very popular and well liked person from the Kenosha (think it was county) board. He has support outside of traditional Democrats. Outside of Ryan's first two elections it was the only time he faced a serious challenger. It was also a perfect storm in the Preaidenrial election that he was on. Then in two years against the same candidate he went back to his normal domination. In summation, he's not losing.
