G consider if it had been Obama asking everybody to leave the room and than saying what Trump said. Trump isn't ignorant, he knew what he was doing. Now why is he so intent on protecting Flynn?
Speaking from professional experience, it is far from uncommon for government officials to discuss with law enforcement (or law enforcement to discuss among themselves) the idea that "this guy had to resign in disgrace/got fired, he probably suffered enough, maybe we should cut him a break." And no one considers it "obstruction.'
And, of course, Comey testified that Trump's request, even if heeded, wouldn't have impeded the Russia investigation.
We tend to forget that the President, not the FBI director, is the federal official ultimately charged with enforcement of federal law. The FBI Director answers to the AG. The AG answers to the President. As such, a president can discuss, or even direct, that a prosecution not occur (see, eg, Obama's refusal to enforce immigration law) without it being obstruction.
While there is actually a part of me that would love to see what happens when the left blunders an impeachment into a Mike Pence or Paul Ryan presidency, I (like Alan Dershowitz) just can't go with the idea that so far there's any credible evidence of an impeachable offense.