Supposedly he was an informal advisor with the Kremlin and has a long history with Russia and Russia was trying to recruit him. TRump is mad about it.
Why are you talking about this as if this allegation is new?? This allegation was already made, it's just that we did not have the exact text of the warrant.
We only have the text now because of a FOIA request that came about because the Republicans and Democrats have conflicting accounts of what was in the warrant.
Specifically the Republicans alleged that the entire basis for suspicion was founded in the Steele Dossier, who's status as op research was not disclosed to the court.
The Democrats allege that there was more than the Steele Dossier in the warrant that led to suspicion of Page.
The released warrant in question only says that "Informant #1" was hired to do research by a "US citizen" and a "business associate", though it is potentially possible that the identity of the citizen as the staff of an opposing candidate is somewhere in the redacted portion, so the Republicans' claims can't be proven.
The closest the unredacted text comes to identifying the Steele Dossier as op research is including Page's statements in his own defense that the allegations against him come from hired private investigators from the Clinton campaign.
The released warrant does not mention any source other than "Source #1", which, through context, is obviously Steele, though it is possible there are more sources in the huge redacted chunk of the warrant that mentions sources other than Steele. Ergo the Democrats' claim is not proven but cannot also be disproven.
So the whole document is redacted to the point that we can't tell from it which side is telling the truth and which is not. Which is probably to be expected.
But props to the FBI on this whole warrant. They've done a great service in getting the Right to actually care about the problem of FISA court abuse.