In December, the leader of California's state senate, Kevin de Leon, made a declaration of war.

"California will never appease those who threaten to undermine our prosperity or deprive our people of fundamental human rights," the Senate President Pro Tempore said, opening the 2017-2018 legislative session after the November 8 presidential election.

That opening salvo was a warning to US president-elect Donald Trump that California, the so-called "Golden State," would at the very least be a headache for his presidency.

California is the most populous state in the country and also the one with the largest population of Hispanics: Of its 39 million inhabitants, about 15 million - 39 percent - are Latinos, a community the incoming US president targeted during his election campaign.

The state is a Democratic stronghold, where Hillary Clinton beat Trump by more than 4 million votes and 30 percentage points.

The Assembly and the Senate, the two chambers of the state legislature, are overwhelmingly controlled by the Democratic Party, which also includes the state's governor, Jerry Brown, and its new attorney-general, Xavier Becerra, who is of Mexican origin.

"We have never in the modern history of the United States had a candidate this repugnant," De Leon said of Trump in a December interview with the Spanish newspaper El Pais.

On that first day of post-election legislative sessions in the state capital Sacramento, California introduced bills to protect the 3 million undocumented immigrants - mostly Mexicans - who live in the state.

It was a challenge to Trump, who based his campaign on promises to expel undocumented immigrants and denigrated Mexican immigrants as criminals and drug traffickers.

Among other things, lawmakers in California have proposed a fund to pay for the legal defense of undocumented immigrants challenging deportation and the establishment of centres to train lawyers on immigration matters.

California is considered a "sanctuary state" for undocumented immigrants, a state that refuses to share information on undocumented immigrants with federal authorities, making it difficult to detain and deport them.

Some "sanctuary cities," including San Francisco, have laws prohibiting municipal employees from cooperating with federal immigration authorities for deportation purposes.

Trump has threatened to cut federal funds to those places as punishment. About a third of California's state funding comes from the federal government.

Immigration is not the only battleground where California is prepared to fight Trump.

Among the state's top priorities are the fight against climate change - which the president-elect has denied - and defending the country's historic expansion of health insurance under outgoing US President Barack Obama.

Even before the inauguration, the Republican-dominated US Senate took the first steps toward dismantling "Obamacare," which expanded health insurance access to 20 million people who lacked it.

"We are not looking for a lawsuit, but we are prepared to defend the values of California," De Leon said in the interview.

- dpa