A head to head comparison of the Maryland 2020 Primary gives us an idea of the break down of the voters.
Joe Biden received 70% (789,753 votes) beating both Donald Trump who received 24% (297,198 votes) and Bernie Sanders who received 6% (81,939 votes).
Joe Biden wins 13 counties in the state of Maryland while Donald Trump won 11 counties.
These 10 counties play an important role in these primary elections. The top counties in the state of Maryland contain many voters. Winning in these counties can allow a candidate to capture many votes. For example, the top county (Montgomery) contains over 6 times as many voters as number 10 on the list (Charles).
Bernie Sanders vs Joe Biden
Joe Biden vs Donald Trump
Donald Trump vs Joe Biden
In a head to head match up on just the total number of votes, Joe Biden (92%) beats Bernie Sanders (8%). Donald Trump (78%) beats Bernie Sanders (22%). Joe Biden (75%) beats Donald Trump (25%).
Joe Biden captured many votes in the top counties in the state of Maryland. Bernie Sanders and Donald Trump did their best in smaller counties but it was enough to surpass Joe Biden's vote advantage. This gave Biden an upper hand in the state of Maryland.