Dynamic inconsistency and subgame perfection

I’m glad Sestak beat Specter in Pennsylvania. I have a great deal of respect for people who have left the Republican Party because it’s been taken over by lunatics, but Specter’s Shawkshank Redemption wasn’t very impressive.

On the other hand, I certainly appreciated having that sixtieth vote for the Access to Care act, and if Specter hadn’t thought that his party switch would save his political skin he wouldn’t have crossed the aisle. So if, the day before Specter switched parties, I’d been told that he would do so only if I and people like me promised to support him, I would happily have made that deal. No doubt the White House had to make that deal explicitly, and I don’t blame them for living up to the commitment.

Since there was no way of binding Democratic activists to such a deal, they went with the better candidate, and Specter is left without the promised reward of his apostasy. In the jargon of game theory, we faced a dynamic inconsistency: the strategy “promise Specter support” wasn’t subgame-perfect, since once he’d defected and couldn’t un-defect it was advantageous to dump him.

On balance, the disadvantage this situation causes for party-switchers is probably a feature, not a bug.

Author: Mark Kleiman

Professor of Public Policy at the NYU Marron Institute for Urban Management and editor of the Journal of Drug Policy Analysis. Teaches about the methods of policy analysis about drug abuse control and crime control policy, working out the implications of two principles: that swift and certain sanctions don't have to be severe to be effective, and that well-designed threats usually don't have to be carried out. Books: Drugs and Drug Policy: What Everyone Needs to Know (with Jonathan Caulkins and Angela Hawken) When Brute Force Fails: How to Have Less Crime and Less Punishment (Princeton, 2009; named one of the "books of the year" by The Economist Against Excess: Drug Policy for Results (Basic, 1993) Marijuana: Costs of Abuse, Costs of Control (Greenwood, 1989) UCLA Homepage Curriculum Vitae Contact: Markarkleiman-at-gmail.com

17 thoughts on “Dynamic inconsistency and subgame perfection”

  1. Could you please define what you mean by "Shawshank redemption"? I've seen the movie, and I STILL don't have the slightest clue what the phrase means to you in this context.

  2. Specter did not have a swell future if he stayed a Reep: Toomey looked like a probably winner in a Specter-Toomey primary. I think his choice was rational, and in fact it nearly worked. One of his big problems was that he is a personally unpleasant man, he didn't have a lot of folks who were loyal to him for him. Last I read, either a Specter-Toomey or a Sestak-Toomey general looked like a close race, so the Dems didn't have a big November reason to go with Specter.

  3. The calculus is a little more complicated than this short precis suggests. Remember that one of the reasons Sestak started his primary challenge was Specter's unwillingness to vote with the democrats after he had changed parties. After the the primary threat he became slightly more loyal to his new party, but his record was still less than stellar.

    So I think that from a game-theoretical point of view this means that switching party label is not actually a strategy; it's the behavioral switch that controls the outcome.

  4. I voted for Specter twice when he was a Republican, and I would have voted for him again as a Democrat if I still lived in Pennsylvania. The problem with the Sestak campaign is the same one as the various Club for Growth primary challenges (including Toomey 2004) — if you assert that those in the center are not "True" Democrats or Republicans, you send them away from your party, and you can't expect their support in the general election. The Club for Growth and its fellow travelers have successfully made the Republican Party into a smaller tent, and it looks like its counterparts on the left may accomplish the same thing.

  5. There's also dynamic inconsistency on Specter's side. He moved left in response to the primary challenge from Sestak, but could've moved back towards the right after he was through with Sestak. If he could have promised to remain solidly in support of the Democratic agenda, he probably would've been happy to make that deal to win the primary against Sestak, but he couldn't make a binding deal so he might have drifted back rightwards. So Democrats couldn't trust him, and that contributed to their support for someone with more solid liberal credentials in the primary.

    Sestak was also polling better than Specter in the general election head-to-head matchup against Toomey, which is another reason to support Sestak. An extremely close Sestak primary win probably would've been the best possible outcome for Democrats, since it gives them the better candidate this time and gives some hope to future switchers.

  6. FloydRayford, you sound like the mainstream media in insisting on balance over truth. Sestak and progressives like him are not the equivalent of the creationists who have taken over the Republican Party. They are the mainstream of the Democratic Party; they are the people who elected Obama and are disappointed in Obama's subsequent Bush-like behavior.

  7. Henry, the plain fact is that there are lots of Pennsylvanians who you apparently would deem insufficiently "progressive", but who nonetheless voted for Obama in 2008 and Rendell in 2006 and 2002 — Specter moderates around Philly and Murtha blue collar types in the West. If the Democrats wish to ignore their concerns relating to things like keeping spending in check, crime, and national security, those voters will not be there for Onorato or Sestak this time around.

  8. Floyd Rayford: Arguing that someone who has served for 30 years as a Republican Senator is not a "true" Democrat may not drive all that many people away.

  9. Obama and the institutional dems owed Specter support for his re-election or else they would never be able to get anybody to switch or otherwise put themselves at risk politically. But rank and file dems, and other prospective candidates didn't owe Specter anything. The party and the people who vote for its candidates do not always have a unity of interest.

  10. I like one little line that Mark says…he has "a great deal of respect for people who have left the Republican Party". You do realize that a sizable portion of the Tea Party folks left the Republican Party because it wasn't "lunatic" enough? Are these the folks you have a great deal of respect for?

  11. Shawshank Penitentiary was the location of Death Row. A "Shawshank redemption" was a term for the miraculous conversion to Christianity of someone under a death sentence and hoping for a pardon.

    To generalize, it's an apparent change of heart motivated by terror. After a lifetime as a Republican, Arlen Specter finally discovered he was really a Democrat when it seemed the only way of saving his political skin. I'm glad it didn't work.

  12. Mark- Concerning Stephen King's fictious Shawshank Prison, I believe you are mistaken about there being a death row located there or at least it isn't mentioned in the story. The story is about an unjustly convicted man dealing with the brutality of life in prison and his eventual escape. (Maybe we could say Arlen Specter escaped the brutality of living in the GOP? No I guess not.)

    I do hate to quible about such a small thing but it is one of my favorite King stories so it grates to just let it go. After all the word 'fan' is short for fanatic so I can't help myself.

    Now back to our regularly scheduled rangling.

  13. It's the story of an innocent man unjustly convicted, who while in prison carefully gains the trust of the prison authorities, in order to abuse it, while planning his escape. I suppose you could make an analogy here, but Specter wasn't imprisoned in the GOP, he was part of it voluntarily. And I think it's been a rather long time since anybody in the GOP actually trusted Specter.

    The lead character in Shawshank was more than a little sympathetic. I don't think anybody is particularly sympathetic towards Specter, though to be fair, Specter himself does manage somehow to tolerate his own presence…

  14. It's a little frightening to hear people (even by implication) painting Sestak as some kind of leftist whom "moderate" democrats wouldn't vote for.

  15. Arthur: By your standards, the tens of thousands of Pennsylvania registered Democrats who have switched parties are not "true" Democrats. In recent years, the Democrats have made significant gains in the Philly suburbs. Would you rather those people return to voting for Corbett, Toomey et al. hereon?

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