Pivotal Politics Model
The Pivotal Politics Model is a social choice theoretic model seeking to explain why (a) gridlock is common in a modern democratic institution and (b) gridlock is broken by large majorities rather than by margins.
Contents
Formulation
Suppose that legislators have a preferred policy position. And suppose that between any two given policy positions, they will favor the one closest to their own preference.
If the legislators' preferred positions can be plotted linearly with the status quo position (q), there will be a median legislator position (m).
If the model stops here and a simple majority voting rule is established, this is fundamentally the median voter theorem; the outcome policy position will be m.
If a filibuster rule is introduced, whereby a policy position must instead pass a cloture vote with some greater threshold, then a filibuster pivot position (f) is added. While a cloture threshold could be placed on either side of a linear space, the median legislator is obviously a member of the majority party, so f is always shown away from the majority party's 'side'.
In one universe, imagine that f is closer to m than q. Far more than a simple majority are in favor of the policy change.
- Otherwise, a position will not pass cloture, and no policy change will be seen.
Going by this logic, policy change is only possible in two circumstances:
- The median legislator is moving the policy position away from the majority party's 'side'.
- The status quo is so far from the majority party's 'side' that a filibuster-proof supermajority is in favor of change.
If a veto rule is introduced, whereby an arbitrary position on the linear space is designated as the preferred policy position of the veto-er, then a veto pivot position (v) is added.
...
If a veto override rule is introduced, whereby some further threshold must be achieved to override a veto, again a pivot is added.
...