it also took on much of the tone of traditional anti-Semitic tropes

I'm not certain what the author means here, nor even that the author is correct about the neocons--but traditional antisemitic tropes (the author has screwed up the word antisemitic) means common stereotypes which promote antisemitic prejudices--that all Jews are greedy, that there are Jewish cabals to manipulate non-Jews, that Jews control the world's financial systems. Those are tropes, common over-used descriptions of Jews which are prejudicial in nature, i.e., antisemitic.

Thanks, so what does "took on" mean here? Does it mean that the neocons has become the target of the traditional anti-Semitic tropes?

In this context, "took on" means assumed the "assumed the appearance or attributes of" something.