Regardless of whether he informed Congress or not, it would have political ramifications. If there had been no ramifications, informing Congress when he did would have been the right choice, hence it was still the right choice.
He only had to inform Congress because he broke with department policy to elaborate on investigations in a bizarre press conference where he offered his opinions and was then forced to testify. He also worded the letter in a vague and scandalmongering way, and sent it to the committee chairmen most likely to leak it and lie about its contents. Pretty much indefensible.