All national debt is funded through the sale of treasury bonds, that is a fact. Even if the Federal Reserve were to directly purchase them (like in the case of quantitative easing), the Federal Reserve is a corporation owned by the commercial banks and therefore the government can’t just print money and spend it. However, the banks can.

Here’s a link to the history of the federal reserve: https://medium.com/@jarljensensocial_76795/history-of-our-financial-system-how-banks-ended-up-in-the-federal-reserve-e1024b75c6eb?source=linkShare-e6bd750eb12b-1526293379