In the months leading up to the election, Trump racked up the miles, crisscrossing the country in support of Republican candidates. It was reminiscent of his 2016 campaign for the White House.
Trump visited nearly half of the 50 states, and some more than once. This graphic shows where he went. The color changes for each additional visit.

He seems to have focused his attention on eastern states, particularly those in the Rust Belt. People in this region were crucial to his successful presidential campaign.
Paul Sracic, professor at Youngstown State University, says Trump went back to the area to solidify the support of non-Republican voters who backed him two years ago. The President wanted to make sure they would show up at the ballot boxes to support his candidates.

Let's see how this worked out.
Trump went to Indiana, where there was a Democratic incumbent senator, four times. A Republican newcomer was able to flip the seat.
But in the other Rust Belt states of Pennsylvania, Ohio, Michigan, and Illinois, incumbent Democratic senators were able to get reelected.

The results seem to indicate that part of the coalition that supported Trump 2 years ago turned their back on his administration during this cycle.
This may be down to working class white people, who supported him in 2016, feeling increasingly dissatisfied with his administration. Experts say they are being hurt by Trump's protectionist trade policies and are not benefiting from the robust economy.