The campaign got a new fillip in January when the state attorney general, Xavier Becerra, approved language for a Yes California-backed ballot measure for the 2018 election, clearing the way for signature gathering. It has also earned about $60,000 in donations, Mr. Marinelli said. The measure would ask voters to remove a reference in the state’s Constitution to California as an inseparable part of the United States and set a second vote, for March 2019, that would ask, “Should California become a free, sovereign and independent country?” But backers need to collect 585,407 valid signatures, a daunting task.

David A. Carrillo, the director of the California Constitution Center at the University of California, Berkeley, is not among the supporters. “California seceding is so unlikely to happen it’s a waste of our time even to discuss it,” Mr. Carrillo said in a telephone interview. “Even if the state could secede, it’s a terrible idea.”

In the United States Constitution, Mr. Carrillo said, “there is no procedure for allowing states to leave, and if you want a practical example, there is the Civil War.”

Still, Mr. Marinelli said he believed the support was there.

A former Republican turned liberal political activist, he said he turned to teaching English in Russia to pay the bills and because his wife is Russian. They met during an earlier teaching stint, and he said he intended to return to California when his contract expires in June.

He co-founded the California secession movement in 2014 in San Diego, flirting first with the name Cal-Leave-Fornia before settling on Calexit, after the successful “Brexit” campaign for Britain to leave the European Union.

While no indications exist of a direct Russian government hand in Mr. Marinelli’s organization, a group that is nominally independent but nonetheless state financed, and supports only causes that dovetail with the Kremlin’s foreign policy, paid for a hotel room in Moscow during a congress of secessionist groups from around the world in September 2016. These included the Texas Nationalist Movement, backers of Puerto Rican independence and a group wanting to restore the Hawaiian monarchy. A Russian group, known as the Anti-Globalization Movement, which like Mr. Marinelli advocates the breakup of the United States, also offered him office space in Moscow to open an “embassy” of California in Russia, and Mr. Marinelli accepted.