Unfortunately, he has become radicalized by these alt-right folks online. He's become obsessed with Jews and white identity politics. His Twitter feed reads like that of an alt-right troll, not that of a person who wants to campaign against a person two heartbeats away from the Presidency. Breitbart indicates they are backing away, although we don't have a formal statement from Bannon yet. I've seen many others back away recently.
I'm not a big fan of Paul Ryan, but at least he has gotten things through the House (many things are held up in the Senate). He's also a viable candidate. If Paul Ryan hadn't have gotten anything through and Nehlen had stayed the same as he was in 2016, he'd have gotten a lot of support. Paul Ryan has, though, and even if Nehlen managed to beat him in the primary, he'd go down like a rock in the general.