Why Did the United States Continue to Support South Vietnamese

Why did the United States continue to support South Vietnamese leader Ngo Dinh Diem's corrupt and weak regime?

A) Diem had the support of his people, which pointed to an eventual South Vietnamese victory over the communists.
B) By 1963, Diem's forces had regained much of the Vietnamese countryside from the outnumbered Viet Cong.
C) Presidents Kennedy and Johnson feared losing Vietnam to communism.
D) U.S. officials were caught by surprise when a military coup led to Diem's death.
E) Diem had built a stable and broad base of support for his government using advice from American officials.