Against an unconventional front-runner, unconventional measures are required.
In the case of Trump, the person most willing to think this way was Ted Cruz, who made a serious bid to induce Marco Rubio to join him in an anti-Trump unity ticket. Would this have ultimately worked? Quite possibly not, but it was a brighter idea than the path that Rubio ultimately took — passionately bemoaning Trump’s ascent but refusing to gamble boldly in response.
There isn’t an obvious unity ticket equivalent for the non-Sanders Democrats, but the dynamic between Bloomberg, Biden and Buttigieg is worth watching. They are all positioned as moderate alternatives to the Sanders revolution, and after South Carolina and Super Tuesday one of them may look a lot more viable than the others. In which case two of the B’s swiftly dropping out and just as swiftly campaigning and fund-raising for (or simply funding, in Bloomberg’s case) the third might be the only chance at a not-Sanders consolidation. And that chance is worth taking because of the third lesson: