LBJ's problem was he didn't really want to fight that war, but didn't want to appear to be soft on the commies. So as a consequence we got all those escalations in the war and so gave the NVA time to adjust. Instead of coming in and bouncing the rubble, or keeping it small.
"Moderation in war is imbecility." Admiral John Fisher, predicting unrestricted submarine warfare in WW-I.
As Ho would say, "Keep it small as you want, we ain't going away."
Iraq delenda est.