A head to head comparison of the Indiana 2020 Primary gives us an idea of the break down of the voters.
Donald Trump got 53% (505k) of the vote to beat Joe Bider (381k votes) by 40% and Bernie Sanders (68k votes) by 7%.
Donald Trump won 83 counties out of the 91 counties in the state of Indiana. Joe Biden won 9 counties and Bernie Sanders did not win any counties. Since Donald Trump won so many counties, he was able to win the 2020 Primary election in the state of Indiana.
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, Joe Biden (85%) beats Bernie Sanders (15%). Donald Trump (88%) beats Bernie Sanders (12%). Donald Trump (57%) beats Joe Biden (43%).
These 10 counties play an important role in these primary elections. Marion county has nearly double as many voters as Lake county. Winning among these 10 counties is greatly beneficial to candidates in obtaining the victory in the state of Indiana.
Since Donald Trump won 83 counties in the state of Indiana, he was able to secure the victory. He did not however win the top counties (Marion, Lake). Donald Trump won because he won so many counties. Joe Biden only won 9 counties in the state of Indiana.
Related References: 2016 Indiana General Election Story, 2016 Indiana Primary Election Story