Today’s parties succumb to the temptation to overreach when in control of an institution. By overreach I mean simply that they attempt to govern in a manner that alienates the marginal members of their electoral majority. Overreach has two components: (1) adopting policies and positions favored by the party base that are more extreme than those favored by marginal supporters and (2) prioritizing issues that are important to the party bases but much less so to marginal supporters. The close party balance encourages a go-for-broke mentality when a party gains control of an institution. The resulting overreach leads to a loss of support in the next election, which contributes to unstable majorities.