“The GOP establishment is in a very precarious position right now. With each passing day, I see a growing likelihood of a scenario where Trump wins the White House and the Republicans lose the Senate”
That would be dumb.
It would also be dumb to win the Senate but not the Presidency.
Vote R across the board and sort it out after there is a Republican White House, Senate and House.
That is when to begin the reorganization - eg Paul Ryan removed as Speaker, assigned a broom closet office down the street etc...
Trump is going to get a lot of support from registered Democrats, and I predict he's going to do surprisingly well among black voters (especially black men). I don't see these people casting a vote for Trump and for a Republican Senate candidate.
This is an interesting dynamic because when Trump gets a lot of traction for his call to "drain the swamp," he's talking about a swamp where the Republicans control both houses of Congress.