I don't dispute the centrality of the US anti-war movement and the courageous resistance of the Vietnamese to the defeat of imperialism - but this itself provoked a crisis in the establishment and split it down the middle.
If you read Gabriel Kolko's excellent "Anatomy of a War" on Vietnam, he documents how capitalists and big business who had traditionally supported American foreign policy for obvious reasons began to grow uneasy about the huge resources going into an unwinnable war - such huge resources that it was imbalancing the whole economy.
From the time of the Tet offensive in 1968 to the end of the war, the dollar was in perpetual crisis and America began to experience several economic problems such as inflation. This combined with the fact that the US couldn't hold Vietnam led some sectors of business to begin to look for an alternative
We might see big business start to do the same in Iraq. Naturally capitalists will support a war to secure the oil fields of Iraq so as to continue US dominance of the world economy - but at a certain point, as Iraq becomes a quagmire and the "vietnamisation" fails, with it clear that huge resources are being channelled into an unwinnable war - some capitalists will begin to agitate for the US to cut it's losses and run.