The most relevant evidence to Kennedy’s claim that the internal conditions of the United States relate directly to the Communist threat is:
"This is a great country, but I think it could be a greater country; and this is a powerful country, but I think it could be a more powerful country."
This statement implies that the strength and greatness of the United States are tied to its internal conditions and suggests that improving those conditions is essential to counter the Communist threat. By emphasizing the need for improvement and growth, it links domestic issues directly to the broader struggle against communism.