Having belatedly recognized the electoral futility of dismissing Obama as a neo-liberal failure, some progressives are now arguing that he was actually a leftist outsider challenging the establishment in 2008. Is that accurate?
No. Obama, as you will recall, had at least as much establishment support as Clinton did in 2008, and the differences between the two on the issues were microscopic. Obama set himself apart from Clinton by pointing to his opposition to the Iraq War, and by arguing that he, unlike the uniquely divisive Clinton, could bring the country together. The latter argument, of course, ultimately proved to be incorrect, but it was perfectly plausible at the time. It also worked to his advantage that we were tumbling into the Great Recession at the time of the general election, and that McCain had no clue as to how to deal with it.
So, no, the success of his campaign in 2008 is in no way a harbinger of success for Warren or Sanders in 2020.