AHC: win the Vietnam War for the US

The corruption is what made the North Vietnamese and the Viet Cong preferred by the people of South Vietnam.

Keep in note the South Vietnamese government was just as corrupt and authoritarian like the KMT under Chiang Kai Shek and South Korea at this period.

1. That would risk intervention by China if North Vietnam was bombed. How well the Chinese would perform in Vietnam on the side of Ho Chi Mihn may not be favorable as we saw what happened in 1979 when they fought against their wayward communist revolutionaries.
2. Well, the Soviets didn't have the navy to projected that far. The deployments to the South Pacific and the South China Sea were limited. The area is controlled by the U.S. and their allies. Much more the U.S has Subic Bay in the Philippines for resupply and maritime patrols. Cubi Point hosted P-2 and P-3 MPAs so any submarine might be caught. The Philippine Navy at this period had anti-submarine capabilities.
3. I don't know exactly what the French left, but it did for sure drift the Vietnamese into the anti-colonialist stance. South Vietnam was ruled by a dictator no less.

I think this would be very difficult since North Vietnam was practically in a state of total war. It would probably come down to how much of a loss it would be for the USA compared to OTL.

1. We did have an operational art for COIN. But we had idiots in charge who did not read our successful history of special operations. Just a brief perusal of the Filipino American War would have been illustrative of what worked and did not.
2. OSS operations in WWII were successful. You have to swim with the fish, not against them, as Mao used to say. 
3. We picked the wrong locals. See 2.
4. See 3.
5. See 3 again.

Part 2. 
1. Air campaigns have to support an achievable objective. Most practical applications of airpower have been based on three plainly limited goals,
a. reconnaissance.
b. temporary (note the word "temporary") restriction of land and sea movement and communication.
c. use and denial of the air for a., b., and c,. 
As a remark about bombing the PRVN into the stone age, that "theoretically could work" if they were that far above the "stone age" in relative terms. They were mainly an agrarian society with very little domestic manufacture. Their infrastructure was very limited and oriented to a "service economy" and not a consumer of goods one. Bombing "them" to put them in the dark, freeze them, famish them and terrorize them had been tried in at least 14 different previous iterations before. Douhet does not work. MAHAN works. You need blockade.        
2. Agreed. Mine their harbors and rivers, drop their bridges. Kill their air force. But refer to 1,. in the doing.
3. You could have talked to Ho, when he first wanted to talk to us. Short of that, the DPRVN is not going to talk to the Americans after 1950. Those are the people we have to convince.