LA Times:

The troubled reality, of course, is the enemy can see the same calendar light and knows it must only wear down and out-wait the notoriously impatient Americans, as the Vietcong did in Vietnam, where American support for its domestic ally withered. And so did the local government’s ability to withstand guerrilla war.

Where to start?
The Viet Cong ceased to be an effective force after Tet, in 1968.
The local governments were quite effective in keeping them that way. In fact there were over a million weapons provided to the local governments in South Viet Nam by the last invasion by the NVA.

The Democrats led by the late unlamented Teddy Kennedy killed a million or two people in SE Asia by wearing down the American people, not the Viet Cong.

History matters.