Vietnam wasn’t lost as an “insurgency”. Tet in ‘68 spelled the effective end of the indigenous Viet Cong in the South. After that, it was infiltration of NVA forces from the North via politically protected routes through Laos and Cambodia that did 95+% of all the fighting in the South.
We didn’t crush the North. Period.
I know that, but Westmoreland tried to do so with Search and Destroy missions that were too cumbersome to be effective. He was the wrong guy for the war, although I do think he tried his best.
If we were doing what Abrams was doing the whole time through, then I think things had potential to be a lot different. LBJ didn’t really care that much though, he only cared about losing face and harming his precious Great Society programs.