The timing of Ocasio-Cortez’s endorsement sends a sharp message to the party establishment and the progressive movement: We socialists are not here for Elizabeth Warren’s reformed capitalism. We socialists want socialism, and we’re not keeping quiet until we get it. Ocasio-Cortez seems to be telling us that Sanders and his movement will still be with us when he’s gone—and that she aims to be the one who leads it…

Both Warren and Sanders want big tax hikes on the wealthy and corporations, single-payer health insurance, free public college, easier union organizing and tougher trade deals. Both have eschewed hitting the large donor circuit, stress that their agendas are designed to empower the poor and working class, and threaten the power of consolidated wealth. Both have scoffed at bipartisan incrementalism.

However, if you are a committed socialist, the differences between Sanders and Warren are crucial. Nathan Robinson of the influential socialist magazine Current Affairs last month detailed his problems with Warren. Some were rooted in tactical concerns that she wouldn’t build a political operation to overwhelm the ruling class, as she’s a “law professor” and not a “movement-builder.” But at bottom, Robinson wrote, “I don’t like to say that I can’t trust Elizabeth Warren, but I can’t.” He pointed to this year’s State of the Union address: “Donald Trump promised that America would ‘never be a socialist country.’ Warren stood up and applauded, as Bernie sat and fumed. This was a very clear ‘Which side are you on?’ moment.”

At a similar moment, Ocasio-Cortez has chosen to remind everyone of which side she’s on.