>>He said he fired Comey over Russia investigation. That is obstruction of justice here in the USA.

Here in the USA I accept that fake news encourages a lay interpretation of the meaning of obstruction to beat on their anti-Trump drum, but actually it's a legal definition requiring several elements including "mens rea" and an "official proceeding" being obstructed. Now you might think a FBI investigation is an official proceeding, but in legal terms, I don't think it is.

In my investigation I started with mens rea that seems quite a stretch, especially if you say he made an unwitting admission on TV- and then the recent SC Marinello v. United States decision seems to require government to show a nexus between conduct and a particular "official proceeding" that must at least be in the offing. To see whether an FBI investigation is the official proceeding being obstructed, my read of United States v. Ermoian says it can't be- because an FBI investigation is not a proceeding before a federal agency within the meaning of the statute. So what is he supposed to have obstructed?

I had thought that one way for Mueller to get Trump for obstruction is to trick him into admitting it- but even that won't fly without an official proceeding to be obstructed. So I'm thinking it's now down to his being trapped in perjury like Flynn and that other one. If my understanding is correct that Trump won't be interviewed but will answer written questions, I can't see him being trapped in perjury and in the absence of a credible crime I don't believe Mueller can force more than this. So I'm thinking Mueller must be drawing to the end of his investigation- based on what I can see, which I agree may not be everything. But obstruction over the Comey thing? IMHO you might as well forget it.