I really hope Obama steps in to help stop this. Even if Biden looses to Trump, he wouldn't necessarily bring the House with him. Bernie looses the House, too. And we have an unrestrained Trump on the loose.
Previous Presidents are loath to get involved in primaries. I think Obama will become a bit more vocal once a Dem candidate is selected. Keep in mind that he is still polarizing, and may not carry the impact that the left wishes for. Frankly, Michelle would probably be a more effective voice than her husband, at least early on. The good guys NEED women to be heavily involved this time around. Without them, we are truly lost. I predict a Michelle/Oprah national tour once a candidate is chosen by the Dems to drum up support from the stronger sex.