FBI Director James Comey has been very clear that viewers of the House Intelligence Committee’s hearing on Russia and the 2016 elections should not “draw any conclusions from the fact that I may not be able to comment on certain topics.” Has that stopped Donald Trump or whichever of his advisers tweeting from the official @POTUS account during the hearing? Of course not.
Comey, in his opening statement:
Please don't draw any conclusions from the fact that I may not be able to comment on certain topics … We need to make sure we don’t give other people clues as to where we are going. We need to make sure we don't give information to our foreign adversaries about what we know or don't know. We just cannot do our work well or fairly if we start talking about it while we are doing it.
He later reiterated that point, and throughout the hearing he repeatedly said he couldn’t answer specific questions from both Democrats and Republicans. Nonetheless, @POTUS:
What Comey says there is “I’m not going to get into either that particular case, that matter, or any conversations I had with the president, so I can’t answer that.” He “refuses to deny” only in the sense that he refuses to answer at all.
For context on the range of questions Comey said he couldn’t answer, he also refused to comment on whether Paul Manafort was Donald Trump’s campaign manager as of July 2016. “I really don't want to answer questions about individual U.S. persons,” he said. “It's obvious from the public record but I don't want to start down the road of answering questions about somebody.”
So, yeah. He won’t answer questions about things on the public record because to answer the question might set the wrong precedent for his other answers, but it’s definitely significant when he “refuses to deny” AKA “refuses to answer at all” a question about a presidential briefing.