On Thursday, Gov. Gavin Newsom will make the first of three post-election visits to California counties that Donald J. Trump won in the presidential race, reaching out to working-class voters in the Central Valley who remain frustrated by economic woes.

The appearance in Fresno, to unveil a new economic development system, comes as interviews and polls have shown that economic and class divisions were key to Mr. Trump’s return to power.

With Democrats still mulling over their presidential and congressional losses, Mr. Newsom said in an interview on Wednesday that his party needed to learn from the recent election and to address the struggles of American workers.

“A lot of people feel like they’re losing their identity or losing their future,” Mr. Newsom said. “Message received.”

A leading Democrat who has been viewed as a potential 2028 presidential contender, California’s governor has long been a pointed critic of Mr. Trump. Over the past two and a half weeks, he has indicated that he expects his state and the Trump administration to repeat the pitched battle they waged during Mr. Trump’s first term, when California sued the federal government more than 120 times.

The governor’s immediate response after the Nov. 5 election was to call his state’s Democrat-dominated legislature into an emergency special session that would start in December. Mr. Newsom urged Democrats to “stand firm” against expected efforts by Mr. Trump to deport immigrants, further limit reproductive rights and weaken environmental regulation.

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