What are the current standards for plagiarism?
If we look at Wikipedia, these seem to be relevant parts here:


  Plagiarism is considered academic dishonesty and a breach of journalistic ethics.


For political speeches of the kind we're discussing, there are near zero expectations regarding academic correctness, or journalistic integrity (not to mention honesty and ethics, which are also part of the quoted sentence).

Any standards are valid only in their respective context. Academic plagiarism and journalistic plagiarism have vastly different standards and consequences. As far as I am aware, there is no standard for plagiarism in the context of political speeches.

and 


  Plagiarism is not in itself a crime, but can constitute copyright infringement


Copyright (usually) allows derivative works, which seems to be what we're dealing with here. 



In other words: You can't plagiarize a political speech.