It’s possible there was some pushback on the manpower levels, because that actually is closer to a military decision. Though apparently even then, the military often just takes what they get. The original plans for the 1991 Gulf War didn’t include the flanking attack from the western desert because not enough forces were allocated, and it was Secretary of Defense Dick Cheney who had to remind the generals that they were allowed to request more troops if they thought they needed them.

But the decision to start and stop wars is explicitly political and there is a much greater taboo against the military trying to tell the president which wars the country should be fighting in the first place. Which is a big part of the difference between a democracy and a military dictatorship!