You know the score when someone switches party. It starts with the very verb. Joining your side = switching. Departing your side = defecting.
Everyone who joins your side is ‘senior’ and has a principled reason. If they’re leaving your side it’s about their recent defeat / deselection / absence from key meetings.
They join your lot for an important policy reason… but they leave your lot only oddly quoting a policy that’s been in place for years and they didn’t object to when they were getting expenses as the committee chair.
All very familiar, save the recent reasons given by a (defeated, see above) Liberal Democrat for switching to the Conservatives in Reading:
No reason really … I was fed up, that’s all.
Mind you, I’d have thought the party for fed up people these days would be UKIP.