This and other differences between Warren and Sanders are bound to become points of hot dispute — and soon. Biden’s lead in the polls once surpassed the combined total of his two left-wing opponents. But not any longer. Together they’re polling at about 34 percent to Biden’s 27. A left unified behind one standard bearer could shake and even shatter the Biden campaign’s desired narrative of inevitability. But a divided left remains in second and third place nationally, with state-level contests primed to be divvied up among all three leading candidates — a recipe for a brokered convention that could well shatter the party altogether.

Victory requires that the left makes a choice. But neither candidate is going to bow out selflessly. Aside from the personal ambition that’s driving them, there are their supporters. Sanders is leading a quasi-spiritual revolution that would end in democratic socialism in America, and those who believe in that aim are deeply devoted to the movement’s leader. Warren, meanwhile, carries all the hopes of the slightly less utopian progressive left along with the pent-up longing of millions of liberal women intensely eager to see one of their own at long last take down the Republicans, and especially Trump.

That means a fight to the death awaits us.