Repetition helps get your point across. Repetition can help things seem more momentous than they actually are. Repetition can get you pumped.

(Repetition can also get annoying if you over use it, so handle with care.)

Lucky for us, though, Truman uses it just right:

I believe that it must be the policy… (74)

I believe that we must assist… (75)

I believe that our help should be… (76)

Truman gets to the climax of his speech where he offers a declaration of his policy views. He repeats the phrase "I believe" three sentences in a row. When you repeat the beginning of a sentence multiple times like that, that's anaphora. In this case, it's also another example of Truman using plain speak, because the repetition is clear, direct, and signals the importance of what is being said.

Not often we get a politician who tells us exactly what he believes and is able to stick to it, huh?