This is a great article about Jessee Jackson’s early days of proposing a single-payer healthcare system in 1988. It gives some real political context as to why the changes to the US healthcare system have failed due to the health insurance lobby.
It points out that Hillary Clinton and, worse, Bill Clinton were corporate Democrats who owed their power to the financial services/health insurance lobby. Author Peter Navarro also correctly notes that the insurance companies/financial services industry is the fourth arm of the US government.
The financial services lobby is the most powerful in Washington. It has the money and access to write bills, get bailouts, and run its businesses on a daily basis by not taking risks since it knows it will be bailed out by the Federal Reserve. Clinton was a neoliberal, and his policies and contacts still control the DNC. 
All this helps explain why the DNC and Hillary derailed the Sanders campaign and how the Dems nominated Joe Biden, who will oppose any progressive programs, including single-payer health care.
See the article here
