@max, I can't imagine you were ok with Pelosi doing that or the "Dear Commandate" letter but maybe you were ok with them and so are ok with the Iran letter too. But I suspect you weren't ok with them and you are ok with the Republicans doing this as some sort of schoolyard get even scheme.
To the contrary, I'd prefer both partys respect the Constitution. None the less, you can't play keep playing by the rules of baseball when the opposition plays football. At some point you realize that you are a patsy if you think that the President and his agencies are going to respect the separation of powers, and will continue to grow more egregious as long as there is no pushback.
Obama pledged that he is not going to let the Senate to play their constitutional role in consenting to a major international agreement, he has refused to faithfully execute immigration law, he did not comply with the law on the Bergdahl trade, dodged the AUMF in Libya, and essentially rewritten portions of ACA, forcing the Republicans to file suit. And when Congress did not pass legislation for climate change, he ordered the EPA do 'create' law (rules) to impose without Congressional approval.
And all the while he has bullied "independent agencies" (FCC), demeaned SCOTUS, and constantly threatened he "has a phone and pen" that can, essentially, make law when Congress does not do as he pleases.
His constant threats, jabs, and expressed ill-will to Congress and others who oppose him has sown the immense desire for pushback - and now that Congress does so with a letter you hear "traitors" and other such nonsense. Obama's provocations and lack of respect have reached a limit for some, and he has only himself to blame for this development.