Two separate problems. When did the North Vietnamese agree that Thieu could stay in office? Well, after the mining and the bombing all summer long, they were trying out various possible concessions on us. I formed the opinion, inconclusively, I formed the opinion that they were very much afraid of Nixon's election and that if by the middle of September the polls showed Nixon decisively ahead that they would probably make a major effort to settle.
I thought it was one of the few miscalculations I saw them make, that they felt Nixon's task would be easier after the election with respect to the Vietnam War than before. I didn't think so. I thought it would be just as hard, if not harder, after the election.
Be that as it may, they dropped the demand that Thieu had to resign on October 8 I believe it was. At any rate, whenever they put forward their comprehensive proposal. And, that, as far as we were concerned, was the breakthrough.
With respect to leaving North Vietnamese troops in South Vietnam, that proposal was already implicit in October, 1970, when we offered a cease-fire in place. That was not coupled with any proposal for the withdrawal of North Vietnamese troops. It was made explicit in our secret proposal of May, 1971.
It was publicly repeated in January, I believe, 1972 in the sense that our Peace Program did not call for the withdrawal of the troops, and only called for a cease-fire so that we did not make an additional concession on the presence of the North Vietnamese troops in October, 1972. We thought that issue had been settled and we concentrated on no resupply and no reinforcement which was the first time accepted by the North Vietnamese in these sessions.