I think Sanders and AOC lean toward MMT but I'm of the opinion that they don't understand why they advocate it. For example their claim that the Trump tax cuts cost the Federal government more than forgiving student debt (https://www.theguardian.com/news/datablog/2019/jun/30/student-debt-loan-forgiveness-bernie-sanders) is really based on a fallacious understanding of tax. According to MMT, the government does not need to tax in order to spend. It spends firsts and then taxes. Costs are spending, taxes are just the means by which governments control inflation. When someone pays taxes there is no real exchange of value, all that happens is that one side of the balance sheet is debited whilst the other side is credited. The government didn't get anything, just the numbers changed. As far as I understand it choosing not to tax one group of people in the form of tax cuts is not an opportunity cost as the government creates money out of nothing anyway. There's an opportunity cost to the individual taxpayer because they can't print their own money, but not to the public. The MMT debate is really a debate between monetary policy, the type that we see when Central Banks manipulate cash rates and UMPs, as advocated by Friedman et al versus fiscal policy, which means tax cuts/raises and government spending as advocated by Keynes et al. What we tend to see nowadays is monetary policy being implemented firstly and when that fails governments enacting fiscal policies until the perceived threat is over (or thy get threatened with losing office) when they switch back to monetary policies. We jump from being Monetarists to Keynesians and back again. Simply because it's politically advantageous for our public representatives and bureaucrats to do so. Something about the State and democracy being a sham springs to mind.