TPM is basically dedicated to the idea that spewing lazy MSM CW narratives is the opposite of journalism and a mortal threat to democracy. Which means that when they fall into them, you get a glimpse of how those narratives are born and perpetuated.
The “still largely unsubstantiated” line is purely a matter of defensive narrative, a response to the right-wing ref-working. That’s why the MSM uses it and it’s not surprising that it gets picked up and unthinkingly incorporated into reporting by people who associate with the regular MSM. And the thing is, no one in either the nearstream media like TPM or the regular MSM has gone back and compared what we know now to the dossier. If they did, they would see that almost all of it is at least consistent with what we know now, they’d see that the “unsubstantiated” portions neatly tie things we do know into a coherent narrative, they’d see that significant parts of it have, in fact, been substantiated, and they’d see that very little of it has been discredited.
Seth Abramson’s has been doing a lot of this work in one to two hundred tweet Twitter threads. It is work that should be read critically and skeptically, and you should always bear in mind that the speculation linking the facts isn’t fact. But it’s fascinating. His problem is that his medium, and his history as a really over the top Berniebro, of the delegate math magical thinking variety, undermine his credibility. And of course, Maddow is deemed inherently lacking in credibility by the MSM because the alternative is admit she’s kicking their ass.
But the real barrier to anyone taking a hard look at it is the pee-tape allegations. As far as most of the people in the MSM are concerned, that is the entire dossier. The slightly more “look how savvy i am” take is that, no, of course the pee tape stuff is the least important part of it, but it has become so associated with the dossier in the public mind that we simply can’t be seen to be taking it seriously lest we risk our precious credibility by trying to inform people that stuff they think they know is wrong.