This was supposed to be the year Republicans shook free of the Tea Party. Tired of alienating voters with radical candidates, went the theory, the GOP would “tone down the crazy” and run moderates.

California didn’t get the memo. Polls say Tim Donnelly, a libertarian firebrand who has vowed to “annihilate” the enemies of freedom, is likely to be the party’s candidate for governor.

The state assembly member from Twin Peaks – a remote, rural community – has roused grassroots conservatives with broadsides against taxes, illegal immigration and government regulation.

“We have tremendous momentum. When you become a champion of the people they’ll follow you to the ends of the earth,” he told the Guardian during a campaign stop this week.

America’s biggest state was hungry for his promise of smaller government, he said. “The Democratic party has been hijacked by Marxist progressives. Americans believe that government is the biggest threat to our future.”

California and the US needed to secure the border and deter illegal immigrants, added Donnelly, 47. “I don’t blame them for coming here when we’re giving them all kinds of free stuff. The very first thing we should do is stop rewarding illegal behaviour, stop incentivising it.”

Such rhetoric has powered Donnelly past Neel Kashkari, a better-funded and centrist rival who languishes in the polls. But it has alarmed some GOP activists, who fear the impact on efforts to rebrand the party.

Latinos, women and young people, in particular, are likely to recoil should Donnelly clinch the nomination, said Lionel Sosa, a Texas-based GOP media guru who advised Ronald Reagan, both Bushes and John McCain.

“We’re making it very difficult to be likeable,” he said. “We have to remember that if people don’t like us they won’t vote for us.”

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