Vermont Sen. Bernie Sanders has opened up a narrow lead in the California presidential race, with support for Massachusetts Sen. Elizabeth Warren dropping substantially in recent weeks, according to a new poll by the UC Berkeley Institute of Governmental Studies.

By a wide margin, likely voters in the Democratic primary election support the two candidates who lead the party’s progressive wing.

But they are divided on their preferred candidate: The poll found that 24% favor Sanders as their first choice, while 22% support Warren in the Democratic election set for March 3, 2020. In effect, the results are an even split, given the poll’s roughly 4% margin of error.

More on the Berkeley IGS Poll Read the full results

Still, the trend is clear: Warren’s support has declined seven percentage points since September’s Berkeley IGS Poll, while Sanders’ has gained five points.

Former Vice President Joe Biden sits in third at 14%, but he has lost six points since September and eight points since a Berkeley IGS Poll in June. Another moderate Democrat, Pete Buttigieg, the mayor of South Bend, Indiana, gained six points in the new poll, with 12% of likely voters listing him as their first choice.

Poll Director Mark DiCamillo said the most striking insight from the results is the continuing fluidity of the race.

“It’s almost as if voters in one poll are trying out one candidate, and they’re not quite comfortable, and then they try out another candidate in the next poll,” DiCamillo said in an interview. “Maybe half of voters are really not quite comfortable, and they’ve been shifting around. … That’s the bottom line in this poll.”

A series of IGS polls released in recent days provides a snapshot of the Democratic race just four months before the Super Tuesday primary election. Some key insights:

• Likely Democratic voters are trending strongly left. Fully 80% of poll respondents have Sanders and Warren as their first or second choice.

• Just under 80% consider climate change and health care top priorities for action by the next president. Climate change was named the top issue by 47%, with 32% selecting reform of the nation’s health care system.

• Among registered voters, 57% support the impeachment of President Donald Trump, with 30% opposed; 13% are unsure or feel it’s too soon to say. A total of 50% support impeachment by the U.S. House of Representatives followed by conviction in the U.S. Senate, which would lead to Trump’s removal from office. Seven percent favor House impeachment, but oppose or are unsure about Senate action to convict the president and remove him from office.

A separate Berkeley IGS Poll, released Dec. 4, indicates broad support for the decision last week by U.S. Sen. Kamala Harris, a California Democrat, to drop out of the race. But DiCamillo notes that 7% of likely voters who had selected her as their first choice have no consensus on a second choice.

“When voters supporting Harris are allocated to the other candidates” based on their second choice, he said, the overall standings “change only slightly, with Sanders at 25%, Warren 24%, Biden 17% and Buttigieg 13%.”

Biden has long been considered a leading candidate in the race nationally, but the IGS poll reveals a paradox about his standing in California.

Among likely voters in the Democratic primary, 29% believe he has the best chance of defeating Trump in the November 2020 general election; Sanders follows at 22%, with Warren at 13% and Buttigieg at 6%. They also see Biden as having the best mix of experience and qualifications to serve as president, though by narrower margins.

At the same time, however, Biden trails the other leading candidates when voters assess who has the sharpest intellectual abilities, best understands their problems and comes closest to sharing their values and beliefs.

“If you look at most of these attributes,” DiCamillo said, “Biden doesn’t appeal to voters. Sanders wins them. … Biden is just not connecting to voters in their day-to-day lives, even though they think he’s probably most qualified.”

The poll on primary election preferences was administered to 1,694 likely Democratic primary voters, in English and Spanish, from Nov. 21 to 27, with the poll released Dec. 5.