but I thought it obvious which bits were novel - that Israel is an enemy of the US and the Vietcong were not.

The Vietcong never existed. They were an arm of Hanoi. And Hanoi was never an enemy in the sense that the US wanted it to be overthrown or lose territory - nor in the sense that US derecognized Hanoi's authority over large parts of North Vietnam. The US seriously undermines the very existence of Israel. It never undermined the communist regime in the North. The squabble between the US and North Vietnam was like a quarrel within a marriage, like the frequent disputes between the Pentagon and the State Department. Indeed, Mencius argues that it was a dispute between the Pentagon and the State Department. In contrast, the dispute between the US and Rhodesia was existential.