During one of my History tuition classes, we scrutinised the exam paper of a secondary school in Singapore. One of the sources is an excerpt from Truman. The question was: "Is this source useless because it is from the President of the United States"?
The school's highest level answer can be summed up thus: the speech is useless because it is biased. Truman was an "ideologically committed Democrat" who wanted to boost his own reputation as the saviour of post-war Europe.
It is a basic rule in History that no source is ever useless. Even a rambling speech by Nobel Peace Prize laureate Donald Trump cannot be said to be useless. The Mad King of America's words give us a glimpse into his mood at that time and his MAGA perspective.
Every source is useful in telling us something. What does it tell us? What does it distort? What does it not tell us?