Judge not the words themselves, but their effect on the audience. The president fully expected that his hundreds of supporters in the legislative branch would stand and cheer, while the justices remained seated and silent, unable to respond even afterward. Moreover, the president’s speech was only released about 30 minutes before the event, after the justices were already present. In short, the head of the executive branch ambushed six members of the judiciary, and called upon the legislative branch to deride them publicly. If you missed it, check the YouTube video. No one could reasonably believe in their heart that this was respectful behavior.
Then there is the substance of the remark itself. It was factually wrong. The Court’s ruling in Citizens United concerned the right of labor unions and domestic corporations, including nonprofits, to express their views about candidates in media such as books, films and TV within 60 days of an election. In short, it concerned freedom of speech; in particular, an independent film critical of Hillary Clinton funded by a nonprofit corporation.
Obama declares war on the SC - Something for the justices to consider when ruling on constitutionality of legislation or admissibility of documents pertaining to the One.