Biden is the Jeb Bush of 2019. The sure thing who'll be done in by sea change in politics which he doesn't understand and with which he can't keep up. My money is on Kamala Harris as the true representative of the ethnic and ideological tribalism that has taken hold the Dems as its drifts ever leftwards and away from the electoral centre of the U.S..
Some of Sanders' and Warren's ideas have some merit. Especially Sanders notion of taxing financial transactions which would control program trading and the growth of derivatives; and the break up of the global investment banks. That had some exposure in the aftermath of the 2008 financial collapse but was done in by the withering lobbying of the financial industry.
I don't think they can compete with the personification of the culture of victimization and death that Harris represents. And Harris would be decimated in the general election. Drawing urban blue voters and leaving the heartland to Trump.