A head to head comparison of the Ohio 2020 Primary gives us an idea of the break down of the voters.
Donald Trump got 47% (683k) of the vote to beat Joe Bider (622k votes) by 43% and Bernie Sanders (143k votes) by 10%.
Donald Trump wins 73 counties in the state of Ohio. Biden trailed behind Trump winning 15 counties with Biden winning nothing in Ohio Primary.
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 (81%) beats Bernie Sanders (19%). Donald Trump (52%) beats Joe Biden (48%). Donald Trump (82%) beats Bernie Sanders (18%).
These 10 counties play an important role in these primary elections. Even if a candidate is not able to win a majority in the larger counties (Cuyahoga, Franklin), they can still win by winning sizable minorities in these top 10 counties.
Joe Biden won the highest percentage of votes in the top counties (Cuyahoga, Franklin, Hamilton, Summit, Montgomery) in the state of Ohio over Donald Trump but not obtained enough votes in the other counties to beat him in the 2020 Primary election in the state of Ohio. Donald Trump achieved a majority vote in other populous counties, securing him the victory over his opponents.
Related References: 2016 Ohio General Election Story, 2016 Ohio Primary Election Story