It is certainly possible to argue this. In South Vietnam, the US had essentially put Diem in power and had been supporting him throughout his time in office. Diem would have had reason to expect that the US would continue to support him. Instead, the US indicated that they would not oppose a coup against Diem (though they did not agree to allow him to be assassinated). Similarly, the Cuban exiles who attempted the Bay of Pigs invasion could have expected more support. President Eisenhower had okayed a plan that would have provided more air and naval support to the invasion. But then President Kennedy scrapped that plan and substituted one that would have much less US involvement. This can certainly be seen as a betrayal.