5) Trump endorses Ryan, both win their elections. Trump tells Nehlen “Now that I’m President, I’m free to endorse you in 2018. Stay ready”.
That's now how this works. Nehlen's set to catch a possible tsunami. The odds of him being able to repeat this upset, even with the support of POTUS (why would the President get involved here?) is highly unlikely. This is Nehlen's shot, and he's doing a good job making the most of it.
If Ryan's not worried, he'd better reexamine the situation.