Trump has been using primaries to get rid of GOP incumbents whom he considers to be inadequately loyal even if they are stronger general election candidates than their challengers. This is another reason some commentators have decided he has no interest in the outcome of the midterms. Is his position reasonable?
From his perspective, yes. There is nothing Trump dislikes more than disloyalty. In the ordinary course of business, the power of a lame duck over his party wanes as he approaches his sell by date. The midterms are Trump’s last opportunity to demonstrate his dominance over the GOP before his party inevitably turns its attention to the succession. Hence, the purges.