> "Despite its ally’s fundamental weakness, the United States might possibly still have won, of course, had it been willing to fully mobilize its own national power. But that would have required raising taxes, calling up the Reserves and other sacrifices that President Lyndon Johnson shrank from asking the American people to make."
...
"But Johnson was the most astute politician to sit in the White House during the 20th century, and he knew that he faced a paradox. As long as the war in Vietnam didn’t demand too much of them and they believed that victory was just around the corner, most Americans would support it. But if Johnson admitted publicly that South Vietnam could not survive without a full commitment by the United States, he knew that support would crumble."
Yes the SV government was autocratic, corrupt, incompetent, and this made it harder for the SV to get on board. But saying that's the majority reason is frankly incorrect. The full power of the US military would have been enough to guarantee victory or stalemate.
Further counterpoint. See the Korean War. Deeply unpopular at home. Most people didn't even know where Korea even was or fully understand why we were fighting. It was one of the major reasons why Truman's approval numbers were so low. S. Korean government at the time under Rhee was corrupt as all hell and undemocratic. In fact most of S Korea's history is undemocratic. S Korean Army units a total disaster for the most part. Yet S Korea still stands independent largely because we never faltered in giving them the military support they needed.
Also Iraq in 2003-2008 was less about winning over the people of Iraq and a lot more to do with other issues such as the refusal to utilize former Ba'ath party members and generals in the formation of the new government. Arguably the worst screw up was the unilateral exit of the US from Iraq under Obama which lead to the chaos we have to deal with now.