Some of the most strident conservatives in President Trump’s orbit have honed and hardened their political identities in California. There is Stephen K. Bannon, the president’s ousted but still influential chief strategist, who was showered with standing ovations when he spoke at the state Republican convention in Anaheim last weekend. And there is Stephen Miller, a senior White House adviser from Santa Monica who has helped shape the White House’s restrictive immigration policy.

Several of the most aggressively pro-Trump media outlets and personalities, which provide a critical line of support between the president and his base, are based in California, like Mr. Bannon’s nationalist-oriented Breitbart News and Michael Savage, a radio host who has raised the specter of civil war if Mr. Trump is removed from office. Two of the far-right’s best-known pro-Trump conspiracy theory peddlers, Mike Cernovich and Charles C. Johnson, work from California.

And California is home to some of the most Trump-friendly academics, who have made the intellectual case for the president’s agenda in scholarly publications like the Claremont Review of Books.