Like I said, some combination of doctors and legislators. If doctors lobbied the laws (or budgetary line items) onto the books and they are still in effect, they still have culpability.

Blaming congress too is fine, but let's be clear: someone has to fight to increase every budget and the AMA didn't just know this when they were structuring their proposal, didn't just count on it not happening, they considered this an implementation detail subordinate to the openly admitted primary objective of propping up physician wages as the Greatest Generation passed. That was always the goal, they were extremely open about it, and about 15 years ago I was attending a talk on demographics in medicine with a primarily physician audience, one of them asked what the plans were to change this to staff up for the Boomer wave (the bump was on the slide, begging the question) and the presenter waved his hand and said maybe they could do something... or not, and then he laughed, and the rest of the room laughed with him.

I'm glad that the AMA has changed their stated position now that it's too late to change course (for the Boomers anyway) and their squeeze is bearing fruit for them and suffering for their patients, but I'll always remember that room full of doctors and doctors-to-be laughing about the prospect of intentionally understaffing for profit. I have it filed in my memory right next to the phone call of Enron traders giggling as they ordered power plants offline to scare up prices, except it's about a million times worse.