Sadly, when someone is as vilified as Nixon became everything he touched gets painted with a "bad" or "evil" brush and much that was good is swept away. I have a rather unpopular liking for Nixon, flawed as the man was. Regardless, I suspect that there would have been no congress, Democrat or Republican, who would have upheld the treaty. America was war weary and congress way too in fear of their jobs to support anything that might see us embroiled in a war in Vietnam again. It was political poison and politicians only care about being reelected. There are a few notable exceptions but they stand out because they are so rare. Had things been different we might have done more in the way of providing supplies, but there is no way we would have put boots on the ground.