Agree. The Dem/RINO coalition is the majority. Collins is up in 2020 and the other two I think 2022, with McCain likely departing the stage much earlier.
2018 is the year to knock out a few RINOs to give the good guys enough cushion to withstand the defection of these three.
They only pull the stunts they do know because they can threaten to switch parties.
Remember Jumping Jim Jeffords? When the GOP retook control, he wanted back and we told him to stick it.
I think McCain is going to pull a Robert Byrd, ie. die in office.