Beto O’Rourke spent Father’s Day six years ago in Tornillo, a tiny settlement about an hour southeast of El Paso. The federal government had set up a tent camp for migrant children who had been forcibly removed from their parents. This was at the high point of the backlash against the Trump administration’s family-separation policy. It also represented the high point of O’Rourke’s campaign against Senator Ted Cruz, who enthusiastically embraced Trump’s policies to the hilt, from family separation to the much-discussed, never fully constructed border “wall.”O’Rourke had planned a last-minute “March to Tornillo”—live streamed, of course—and had somehow attracted a crowd of hundreds who’d traveled from across the state, were angry at the administration, and wanted to demand humane treatment for the migrants in…