A head to head comparison of the 2020 California Primary gives us an idea of the break down of the voters.
Donald Trump received 30% (2.2M votes) beating both Bernie Sanders who had 28% (2M votes) and Joe Biden who had 21% (1.6M votes) in the overall count of votes in California if the election were among these 3 candidates.
Donald Trump wins 45 counties out of the counties in the state of California to support his claims of his movement in the country. Bernie Sanders won 11 counties and Joe Biden won just 2 counties in the state of California.
These 10 counties play an important role in these primary elections. If a candidate, can get a sizable majority, it becomes very difficult to win majorities in the smaller counties with out voter out reach and increased voter participation in them.
Bernie Sanders vs Joe Biden
Joe Biden vs Donald Trump
Donald Trump vs Bernie Sanders
In a head to head match up on just the total number of votes, Bernie Sanders (56%) beats Joe Biden (44%). Donald Trump (52%) beats Bernie Sanders (48%). Donald Trump (58%) beats Joe Biden (42%).
Donald Trump simply won the majority of the top 10 counties. Joe Biden and Bernie Sanders could not achieve a victory since Donald Trump captures so many voters across most counties.
Related References: 2016 California General Election Story, 2016 California Primary Election Story