It's now generally accepted, if not 100% proven, that the Trump Tower meeting between Trump campaign officials and a mysterious Russian woman was set up by Fusion GPS. Among other evidence, the woman met with Fusion GPS both before and after the meeting. And, of course, Fusion GPS was working with the Hillary campaign and Christopher Steele to convince the FBI to investigate the Trump campaign for Russian collusion that did not exist.
As far as I know, this is new information, and it would be devastating to the FBI's narrative if they were directing Sater to encourage deals with the Russians while they were trying to investigate the Trump campaign for Russian connections. And, yes, the Russian building angle has been used in various Democrat attempts to smear Trump, most particularly with respect to Cohen's congressional testimony.
And, conveniently, Sater was mentioned in the Mueller report several times but not his status as an informant. That's not necessarily surprising (it's reasonable to put a high priority on protecting the names of sources) but when those sources are being used to entrap innocent people and conduct a political coup, the public interest outweighs the secrecy.