They really don't have to in this case Coop. However for them to ask for a transcript of that meeting, when their source allegedly already has the goods to bring Trump down is what's really silly.
What do they need a transcript of that meeting for if this source already has told them what they want to know about whatever it is Trump said revealing our classified info?
In this case, I'd name my source(s) since Trump is accusing them of making this up. I'd smoke him out...tell him "OK...so and so says X now what do you say counter to that?"
Moreover, they should at least corroborate thier source since the charge is so explosive.
When I was taught Journalism at WVU, we were told to confirm all unnamed sources with at least two independently verifiable alternative sources. Three is better, but at least get two more to cover your ***.
In this case they have three denials (Trump, McMaster, and Tillerson) but no backup for their original allegation. Yet they are clinging to the allegation, and demanding a "transcript" of the meeting they are alleging the damaging information they are asking for came from (through their own single source)
It's just bat sh*t crazy Coop! Not the way Professors Cremer, Kearns, Ours, and Stewart taught this little cub reporter to do my job back in the day at good 'ol WVU.
Erick Erickson, a conservative from down your way, knows one of the sources:
I tend to take these stories about the President with a grain of salt. We have seen key details of a number of salacious stories retracted within 48 hours. The media hates the President so much that they’ll run a negative story about him without very much provocation. Anti-Trump sources embedded within the administration in the career civil service, etc. will leak to the press and confirmation bias sets in.
What sets this story apart for me, at least, is that I know one of the sources. And the source is solidly supportive of President Trump, or at least has been and was during Campaign 2016. But the President will not take any internal criticism, no matter how politely it is given. He does not want advice, cannot be corrected, and is too insecure to see any constructive feedback as anything other than an attack.
So some of the sources are left with no other option but to go to the media, leak the story, and hope that the intense blowback gives the President a swift kick in the butt. Perhaps then he will recognize he screwed up. The President cares vastly more about what the press says than what his advisers say. That is a real problem and one his advisers are having to recognize and use, even if it causes messy stories to get outside the White House perimeter.
I am told that what the President did is actually far worse than what is being reported. The President does not seem to realize or appreciate that his bragging can undermine relationships with our allies and with human intelligence sources. He also does not seem to appreciate that his loose lips can get valuable assets in the field killed.
You can call these sources disloyal, traitors, or whatever you want. But please ask yourself a question — if the President, through inexperience and ignorance, is jeopardizing our national security and will not take advice or corrective action, what other means are available to get the President to listen and recognize the error of his ways?
This is a real problem and I treat this story very seriously because I know just how credible, competent, and serious — as well as seriously pro-Trump, at least one of the sources is.