Unless Castle would have bolted...which was a distinct possibility.
If we’re going to trade in possibilities, then there’s a possibility that Obama will have a revelation and become the second coming of Reagan, too...
Small, microscopic chance of that, but it can happen.
I prefer to trade in reality and results in the real world, not possibilities and what-ifs. Castle most likely would have stayed with the GOP, and we could be talking about Senate Majority Leader DeMint or Inhofe or Burr, rather than another few years of Senate Majority Leader Reid.