In his quasi-blog* at The Atlantic, James Fallows asked whether anyone can name a more stupid policy that passed with bipartisan support during the last 50 years than the McCain-Clinton proposal for a gas-tax holiday. His pick from the many submissions he received is the mandates and subsidies for corn-based ethanol. The full list of popular submissions is worth reading -- Fallows notes that while some of them had worse effects than ethanol subsidies, in order to make the short list, a policy had to be obviously bad even without the benefits of hindsight.
The policy that I was surprised not to see on the list is the mortgage interest deduction, the one policy that everyone from the Center on Budget and Policy Priorities to the American Enterprise Institute agrees is terrible policy. It's expensive, regressive, and most people agree that it makes homeownership MORE expensive for the people likely to be on the margin between owning and renting. I don't know if it misses the 50 year cut off, or if Fallows' readers are likely to be in the group that benefits from it, and so are blind to its faults.
What else would you put on the list?
*It's a quasi-blog because it doesn't allow comments. This is clearly Fallows' choice rather than The Atlantic's because Yglesias has a real blog on their site.