Unless I read it wrong (the whole article) he is putting out a strong suggestion that the USA should have allowed Hitler to do what he wanted.
I doubt you read it wrong.
Like Germany in 1941, Iran has declared war on the USA, but a long time ago, and most recently repeated it back in January of this year. Do we really have to let every such declaration go unanswered?
I didn’t read the whole 1977 article, but from the excerpt I took that Hitler’s success was enabled by his eventual opponents’ weakness. I don;t know if Buchannan is referring to German and Austrian leaders, or if he is including the likes of Chamberlain and other foreigners.