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Krehbiel: Pivotal politics

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Krehbiel. 1998. Pivotal politics.

In brief

Krehbiel calls his model pivot politics theory because in collective choice settings where issues are well-defined and decision-makers' preferences are well-ordered, a specific decision-maker is shown analytically to be pivotal to the final policy choice. He argues that divided government does not explain why and when gridlock will occur (i.e. parties don't matter), but that his model of pivotal voters does, in addition to explaining why bills pass with greater than minimum-majority size. (This is more or less a quote from ch 1.)

Research Question

Why does gridlock regularly occur in Washington? (Attempts to explain what he defines as two basic facts: (1) Gridlock usually occurs but not always; (2) Winning coalitions are almost always bipartisan and usually greater than minimum-majority sized.)


Gridlock occurs regularly because of moderate status quo policies, supermajority procedures, and heterogeneous preferences. Winning coalitions are usually greater than minimum-majority sized because of supermajority procedures.

The Model

The model assumes that all players can be arrayed along a unidimensional policy space. Parties are not a party of the model, and the status quo is assumed to be exognously given. Furthermore, the game is not repeated (formally).

Players: The most important "pivotal players" are the median member of Congress (not clear which house), the (Senate) filibuster pivot, the veto override pivot, and the president. Although there could be a veto override pivot and a filibuster pivot on either side of the median pivot, the only relevant players are the veto override pivot on the same ideological side as the president and the filibuster on the opposite side.

Sequence of play: Intuitively, it works something like this. The median pivot moves first, choosing either a new policy or the status quo. The filibuster pivot then decides whether to sustain or block a filibuster attempt. Next, the president decides whether to veto. If he signs the bill, the game ends; otherwise, the veto override pivot decides whether to override the veto. Gridlock can occur at any stage; the places where gridlock can be broken are (1) if the president signs the bill or (2) if the veto override chooses to override the veto.

Equilibria: The figure on pg 35 summarizes the general theory. Assuming the president is to the right of Congress, then you have preferences ordered as F - M - V - P. (Note that the veto override pivot and the president might be reversed; if so, substitute "P" for "V" in the discussion below.) As shown in figure 35:

  • If the status quo is far to the left of F, then the outcome is M (since everybody prefers M to the status quo)
  • If the status quo is to the left of F but closer to F than M is, then the outcome gets closer to F (b/c M has to make concessions to get F to go along).
  • If the status quo is between F and V, then you are in the gridlock range and policy will not be changed:
    • If the status quo is at F, then F uses his "veto power" to prevent any change at all.
    • Similarly, if the status quo is at M, then M refuses to change things.
    • Finally, if the status quo is at V, then V refuses to override any vetoes.
  • As the status quo moves to the right of V, then policy can move again, and it will slowly move back towards M.
  • Once the status quo is as far from V (to the right) as M is (to the left), M will be the outcome. For any status quo to the right of this point, M is the outcome.


Since the gridlock range includes all status quo points between F and V (or P), this implies that moderate policy proposals will tend to fall in the gridlock range. Thus, it isn't surprising that presidents often have a brief "honeymoon." Their election changes the alignment of preferences, so some policies that were inside the gridlock range (by the end of the previous president's term) might now be outside of this range, allowing the president and Congress to rapidly identify these policies and move them into the gridlock interval. But after this brief burst of activity, the president will find a decreasing number of policies that can actually be changed given the current alignment of preferences.

Moreover, those changes that are made will tend to be incremental. Unless the status quo is quite far from M, the result of policy change isn't likely to be M; it is more likely to be close to F or V (or P). Thus, despite initial excitement about a candidate's bold proposals, the realities of pivotal politics are likely to mean that actual policy changes will be incremental and passed by supermajorities.

Place in Literature

In General, Krehbiel argues against party-centered theories (numbers 1-4 below), and also against other social choice theories (numbers 5-6):

  1. Responsible party government: cohesive parties always enact the platforms on which they run (Schattschnieder 1942, APSA 1950)
  2. Conditional party government: descriptive theory arguing that the strength of a party depends upon its legislators' preferences. If the parties' members have distinctly different preferences across parties but homogeneous preferences within parties, then the major party is predicted to be sufficiently strong to pass skewed or noncentrist outcomes. (Rohde 1991; Aldrich 1995; Aldrich and Rohde 1995)
  3. Divided versus unified government: Split party control of the White House and Congress leads to gridlock. Unified control leads to legislative productivity. (Sundquist 1981, 1988; Cutler 1988; Kelly 1993)
  4. Cartel theory: Party leaders use negative agenda control to ensure that only those bills supported by a majority of the majority can pass (Cox and McCubbins 2003).
  5. Median voter theorem (Black 1958) (Krehbiel's argument is similar, but looks at why it isn't always the median voter that wins.)
  6. Majoritarian chaos (Aldrich 1995) and stability inducing theories (Ferejohn 1986; Weingast 1989)

Arguing on the same side as Mayhew (1991): the legislative outcomes of divided and unified government are about the same.