The way that the Republicans win the senate in November is campaigning as Republicans, and doing so with a clear agenda. Yes, all elections are local, but there are hundreds if not thousands of things to hit the Democrats on as a unified front.
So if Sessions wants to be majority leader, or if anyone wants to be majority leader, how about assuming the position right this instant and all the way through to November, pushing against this administration, the massive overreach by federal departments, and actually fight these Democrats!
Those fighting this government have been Sessions, Cruz, Lee, and...sometimes...Rubio and Paul depending on the subject.