Sentence:  The pendulum lists the seats from least <WSD>marginal</WSD> to most <WSD>marginal</WSD> for the government on one side, and least <WSD>marginal</WSD> to most <WSD>marginal</WSD> for the opposition on the other side. 
Meaning of the word marked with <WSD> tags:  Subject to a change in sitting member with only a small change in voting behaviour, this usually being inferred from the small winning margin of the previous election.