Idioms are like ninjas. When they work correctly, you don't even know they're there:

I do not believe that the American people and the Congress wish to turn a deaf ear to the appeal of the Greek Government. (6)

While it sounds like something we might "hear" all the time, the phrase "turn a deaf ear" is an idiom that means to refuse to listen to or ignore. Truman knows the American people don't want the people of Greece to think we're ignoring their cries for help. That would be mean and go against our sense of duty as a global power and our general moral compass. (Sort of like the feeling we get when we forget to call our grandparents on their birthdays—we don't mean to be bad grandkids, it's just that it's hard to call people who still think you need to shout into the phone in order to be heard.)

Ugh, now we're feeling bad. Way to use a rhetorical device to put us on a mega-guilt trip, Truman.