There’s little doubt that Trump will handily win Kansas in 2020. It is highly unlikely there will be enough ticket-splitting downballot for the Senate race for the Dems to prevail.
Also, the Dem field in the running is pretty piss-poor. Nancy Boyda appears the leader (at the moment) of declared candidates, and she was a fluke single-term member who ran a very sleazy guilt-by-association campaign attempting to link incumbent Jim Ryun with Mark Foley’s scandals way back in 2006. She couldn’t even hold the seat when Zero won in 2008, losing to Lynn Jenkins.
Rumor has it that Sebelius might come out to run against Kobach.