The map above shows the turnout and the candidate that won each county in the 2018 Senatorial election.  Jon Tester did not win a single county where voter turnout was high, whereas Matt Rosendale won six counties where voters turned out in droves.

The chart above shows the total votes (x axis), the turnout (y axis), and the margin of victory (intensity of color and size of circle) for each county in the state of Montana.  Jon Tester won two of the three largest counties as indicated by the blue circles to the right (just under the legend) with moderate margins.  Matt Rosendale, on the other hand, won the majority of small counties (on the left of the chart) but with large margins.  Rosendale also won the largest county, but with a very slim margin (small circle at the far right end).  Rosendale also won counties with the largest voter turnout.