If Trump wins, the Senate will be o.k. We’ll retain FL, NH, OH and PA. Probably lose IL. Might lose WI. Might pick-up CO and NV. Figure break-even, though maybe a small change either way.
But if Trump loses, we’ll probably lose our majority.
So, this one’s for the Presidency, the Supreme Court and the Senate.
Regarding Iowa - a vacancy would be filled by appointment by the Governor (who is a Republican). The appointee will serve until the next regularly-scheduled statewide election (which would be 2018).
Don’t some states have off year elections in which they will elect an interim senator even after the governor makes a temporary pick?