This would only apply to the Senate, as all members of the House share the same two year term, and it is up at the same time for all.
As elections near, meaning the last two years of a six year term, the Senator in question, starts looking at both his base, and the voting habits of her/his state, and how they have changed in the past six years, plus the present political climate. Then as a rule, the Senator tends to either go harder edge, if their state requires it, or leans towards the center, if that is necessary.
Most of all, it means a strong desire for no serious or hard votes to be had by them during the last two years before the election. Those general rules determines which coalitions , if any, the Senator will join.
