A majority of American doctors now support nationalizing healthcare... but so what? 99% of teachers support public education and we can see what a miserable failure that institution is. The decision on whether or not to nationalize the healthcare industry is primarily a question of economics, not medicine, and doctors have plenty of selfish reasons to support a federal takeover.
There have been many news stories over the past few years about doctors quitting their profession for various reasons, mostly to do with malpractice insurance/litigation and over-regulation, so it's no surprise that doctors are itching for some sort of change. Unfortunately, no one is seriously considering change that would actually improve healthcare and not just health insurance, so disgruntled doctors and patients are left with little outlet for their frustrations other than the proposed nationalization.
Regardless of what a majority of doctors think, nationalized healthcare would be a disaster economically, and consequently a disaster medically. The law of unintended consequences demands no less.