Paul Ryan. AP Photo/Evan Vucci

Last Sunday, former Republican vice-presidential nominee Sarah Palin delivered a warning shot to the man who ended up in that spot on the ticket four years after she did.

House Speaker Paul Ryan, Palin said, was on his way to being “Cantored.” It was a reference to former House Majority Leader Eric Cantor, who lost his seat in a stunning primary rebuke from conservative voters in 2014.

Ryan's "political career is over but for a miracle because he has so disrespected the will of the people," she said on CNN, in a reference to Ryan's refusal to immediately support Donald Trump after he became the presumptive GOP nominee.

"And as the leader of the GOP, the convention, certainly he is to remain neutral, and for him to already come out and say who he will not support is not a wise decision of his," she added.

The unification of his own party isn't the only Republican challenge Ryan is facing this election cycle. Ryan, a nine-term congressman serving Wisconsin's 1st congressional district, is also dealing with a primary opponent.

Paul Nehlen, his challenger, is facing an enormous uphill battle — one poll showed him trailing by 64 points before the August 9 primary. But he has gained attention from some Trump-aligned Republicans frustrated with Ryan's refusal to get in line behind Trump.

Palin and other conservative activists are throwing their support at Nehlen, for whom the former governor of Alaska said she'll do "whatever I can."

"This man is a hard-working guy, so in touch with the people," Palin said. "Paul Ryan and his ilk ... They feel so threatened at this point that their power, their prestige, their purse will be adversely affected by the change that is coming with Trump and with someone like Paul Nehlen, that they're not thinking straight right now."

Nehlen, a Wisconsin businessman, is championing policy positions that are aligned with those of Trump. He pushes an anti-free-trade, tough-on-immigration, reduced-spending agenda, touting jobs he returned to the US from Mexico and Canada.

Paul Nehlen. paulnehlen.com Staunchly opposed to the Trans-Pacific Partnership deal, Nehlen suggested it would create a "super-national commission" among the nations that are a part of the pact.

"Essentially, we would forfeit our sovereignty as a nation," Nehlen told Business Insider in a recent interview. "Stop and think about that for a minute. We would have one vote. Vietnam would have one vote. All the other countries would have one vote. Why would we level ourselves with Vietnam? It's absurd."

Nehlen also chastised Ryan for the omnibus spending package he helped to pass late last year.

"He's been portrayed as a budget guru ... economics guy," Nehlen said. "What demonstrable thing has he done in his 18 years in Congress with that economics degree? Zilch. Zilch."

Nehlen wasn't always staunchly opposed to the House speaker. He said he "pounded signs" and "made phone calls" for previous Ryan campaigns.

That is largely still a trend back home for Ryan, who boasts one of the largest campaign war chests in the nation.

He beat his last primary challenger by a massive 94% to 6% vote in 2014. His favorability among Wisconsin Republicans hovers around 70%, according to a recent poll. When just the Milwaukee media market is taken into account — which contains almost all of Ryan's district — that number inflates to nearly 80%.

"The bottom line is you look at Cantor and say, 'Could it happen?' Well, I suppose it could happen," Charles Franklin, a pollster at Marquette Law School, told CNN. "But there's not the early warning signs that you look for."

Sarah Palin. Screenshot/CNN

For its part, Ryan's staff doesn't seem particularly concerned about the challenge from Nehlen.

"People in southern Wisconsin know Paul Ryan, and they know what he stands for," Zack Roday, a Ryan spokesman, said in an email to CNN. "Janesville is his home, and his commitment will always be to the people he represents."

Yet Nehlen has attempted to take advantage of the evident rift between Ryan and Trump. Nehlen announced his support for the Manhattan billionaire after the House speaker said earlier this month that he was "not ready" to support the presumptive nominee. Although the two held a meeting on Thursday that they described as a "very positive step toward unification," Ryan still did not throw his support behind Trump.

Regardless of whether Ryan eventually decides to endorse Trump, Nehlen said the speaker already "showed his true colors."

"It wasn't an, 'I'm standing on my principals,' as much as it was an, 'I'm going to ignore the will of the voters,'" moment, he said. "That's what he's doing."

"It's just despicable, I think, for Paul Ryan to disrespect the will of the voters," he continued.

Nehlen originally supported Ted Cruz, a Texas senator who won April's Wisconsin primary but recently dropped out of the race after losing in the Indiana primary. He said he switched his support to Trump because he is "going to respect" the voters.

Nehlen seemed to realize the uphill climb necessary to overtake the highest-ranking Republican in Washington. But he said he feels that with an electorate angry at Washington and high-profile support from people such as Palin, his odds are improving.

"Pop some popcorn, sit back and watch," he said. "It's going to be interesting."