It’s not talked about much anymore, but that’s pretty much exactly what happened in early November, 1963. South Vietnamese president Ngo Dinh Dien was captured by a group of ARVN officers and assassinated along with his brother, Ngo Dinh Nhu, the next day.
The U.S. denied any knowledge or involvement in the coup, but it was later revealed that America had assured the ARVN insurgents they would not interfere with the removal of Ngo…
The North Vietnamese government was caught by surprise and said very little immediately. After mulling it over, they decided the coup was a colossal mistake by the U.S. and that any successor government in South Vietnam would be inherently unstable and weak.
With American urging the military first installed Ngo’s Vice President as leader, but within a week, junta leader Duong Van Minh was named president and chief of the military, with new president Tho downgraded to prime minister. The pro Ngo National Assembly was dissolved, and the 1956 Constitution was suspended. The U.S. formally recognized the new government.
It turned out North Vietnam’s assessment was on the mark. The new government foundered and Minh was deposed in a bloodless coup by General Nguyen Khanh in January 1964.
And the war went on.