To me this is the defining reason that his office had to be searched for the documents.
His arrogant attitude towards a subpoena was a blatant act of a person that feels that they are above the law.
If you don't answer a subpoena, you suffer the consequences.
Even if you are part of the elite ruling class. Oops, there is no ruling class in the USA...
This needs to be brought up every time people complain about removing documents from his office. He was obviously hiding them and breaking the law by doing so.
Every story I've seen mention it, it was just a one liner , buried past halfway in the article.