Why do politicians not solve social problems? One reason, of course, is that such problems are intractable. But there's another reason - politicians sometimes lack the incentive to do so because politicians need to keep their enemies alive just as parasites need to keep their hosts alive. A new paper (pdf) by James Robinson and colleagues says:

We develop a simple political economy model of this need for enemies, showing how a politician who is good at undertaking a particular task has an incentive not to complete it fully since he needs to keep the task alive in order to maintain his strategic advantage in an election.

They point to the example of Colombian president Alvaro Uribe, who was regarded as the best man to fight Farc insurgents. His fighting against Farc diminished after Farc was weakened, with the biggest decline in anti-Farc activity in areas with more swing voters.This is consistent with Uribe keeping Farc alive in order to maintain his electoral advantage as the best man to fight Farc. Had Uribe quashed Farc, he'd have lost his political purpose - just as Churchill lost his after the UK won WWII.

This is not the only example of politicians needing enemies. Tyrants and demagogues have always fomented hatred of minorities, and have justified repressson by pointed to the (exaggerated) threat from external or internal enemies. But democratic politicians have done similar things. The Cold War gave Macartyites a reason to justify repressing the left; Argentina's invasion of the Falklands gave Thatcher the chance to fight a war that would double her poll ratings; neoconservatives define themselves against Islamism;and leftist governments need to keep people relatively poor in order to claim to be fighting poverty and inequality.

This last example comes from a paper by Gilles Saint-Paul and colleagues, who provide another model in which politicians have incentives not to do what they are ostensibly elected for.

Of course, politicians do occasionally do the right thing even if it means electoral oblivion (FW de Klerk?), and can sometimes reinvent themselves and so survive the loss of their enemy (Sinn Fein?). But the point here is that politics can sometimes give us bad incentive structures. And this, surely, increases the already-high likelihood that politicians will let us down.