Political rookie Paul Nehlen's longshot bid to unseat House Speaker Paul Ryan is the unexpected highlight of the Wisconsin primaries Tuesday.

Ryan, a Republican, rarely even has a primary challenger. But Nehlen's unexpected boost from Donald Trump made the race one to watch just in case the unthinkable happens and Ryan becomes the first House speaker to lose a primary.

Nehlen, water-filtration company executive, is running his first campaign against the highest-ranking Republican in the country. Ryan has outraised him 17-1 and is endorsed by the National Rifle Association, Wisconsin Right to Life and all 16 GOP legislators in the district.

But Nehlen got plenty of national attention last week when Republican presidential nominee Donald Trump praised him and said he wasn't ready to endorse Ryan, who is immensely popular in his district. Trump relented a few days later.

Despite Nehlen facing long odds, political observers point to  House Majority Leader Rep. Eric Cantor’s stunning Virginia GOP primary loss in 2014 to a Tea Party-backed challenger.