"I really do think Gov. Brown has created a new norm of expectations in terms of fiscal discipline," the Los Angeles Times quoted Newsom as saying. "It's incumbent upon the next governor to model that."
Brown, the state's longest-serving governor, leaves office in January with a state forecast to have a surplus of billions of dollars in the 2018-19 financial year. When the Democrat assumed office in 2011, the state faced a $27 billion deficit. He had been elected as governor two times in the 1970s.
Brown has been a frequent critic of the Trump administration over issues including immigration, the environment and health care. After the administration sued California in March for its so-called sanctuary state laws protecting undocumented immigrants, Brown charged that the federal government was "basically going to war against the state of California."
Newsom was in San Diego on Monday for the final day of his week-long bus tour and vowed to "push back" against the Trump administration if it becomes necessary, including to stop oil drilling off the coast or to protect the state's right to environmental protections.
Last week, Newsom told reporters he also planned to be more active than Brown on certain issues, including on health care and the homeless crisis gripping the state. About one-quarter of the nation's homeless population is in California, and the problem along with the shortage of affordable housing statewide, has been a major issue in this year's governor's race.
According to the Berkeley poll, Cox gets about 50 percent support among "conservative voters" while Newsom had 56 percent support among "liberal" voters. The poll released last week also shows that among early voters, Newsom was backed by 38 percent to Cox's 23 percent and Allen's 14 percent.
"I think the politicians in Sacramento are creating a war with Washington because they don't want people focusing on what they made a mess of in Sacramento and in this state," Cox told reporters in San Diego on Monday.
For his part, Allen has run on a campaign positioning himself as "the only true conservative" and pointed out that Cox didn't vote for Trump in the 2016 election. Cox, who made his money in the housing business, said in a debate last month that he regrets not voting for Trump and has knocked Allen as "a typical politician."
Regardless, if Cox's polling lead against Allen and Villaraigosa holds, he will face off against Newsom in November's election.
"The recent polling here shows very few undecided people in this [gubernatorial] race," said Stephen Goggin, a political science lecturer at San Diego State University. "So I think it's not going to be that surprising with Gavin Newsom and John Cox making it into November. But nothing is done until people actually vote."
If that happens, political observers say, Cox will need to pivot beyond registered Republicans to win the gubernatorial contest in the November general election against a Democratic challenger such as Newsom.
Registration of Republicans in California has fallen since 1997, from 36 percent back then to about 25 percent as of January 2018, according to figures from the state. Democratic registration as of January 2017 was nearly 45 percent of the state's total registered voters while "no party preference" was 25 percent, up from just 11.9 percent in 1997.
"The arithmetic is against the Republican Party," said USC's Bebitch.
She pointed out that the large percentage of voters identifying themselves with "no party preference" in California means the GOP faces an uphill battle to win the governor's office.
"We had a Republican governor not too long ago," said McGhee. "But it has to be an exceptional kind of Republican running a particular kind of race. And whether Cox can run that kind of race is kind of the open question."
The state's last Republican governor was ArnoldSchwarznegger, who has become a critic of Trump. Schwarzenegger enjoyed strong name recognition as an actor and pushed to promote California trade ties and environmental protections.
Cox has said he wants to repeal the California Environmental Quality Act, which is designed to protect the environment. The candidate said measure has contributed to the state's shortage of affordable housing, including apartments.
At the same time, Cox is a critic of the so-called sanctuary laws that protect undocumented immigrants and has backed Trump's plan for a border wall. In contrast, Newsom has called Trump's wall "a monument to stupidity" and been a strong supporter of the state's sanctuary law policies.
Cox also has been a critic of California's gas tax hike and was behind an effort to gather signatures for a statewide initiative to repeal the increase in gas taxes and vehicle fees. Last year, California's Democratic-controlled legislature approved raising the state excise tax on gasoline by 12 cents per gallon, or a 40 percent increase.
Opposition to the state's sanctuary laws and a push to repeal the gas tax could help lift GOP turnout Tuesday and again in the November election. One state lawmaker who voted for the higher gas tax is facing a recall challenge Tuesday.
A USC Dornsife/Los Angeles Times statewide poll released last month showed 51 percent of registered voters support repeal of the state's new gas tax hike.