This is a great article about the early days of proposing a single-payer health care system by Jessee Jackson in 1988. It gives some real political context to why the changes to the US health care system have not succeeded 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. They have the money and access to write bills, get bailouts, run their businesses on a daily business by not taking risks since they know they 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.