Ohr's wife worked for Fusion GPS and apparently seems to be (this means I'm not sure for the trumpanzees) the conduit for the transfer of the dossier to the FBI.
Portions of the dossier have been confirmed.
The FBI obtains evidence from a source that's been credible in the past that trump might be able to be blackmailed by the Russians. Trump is already known to have people working for him in the campaign with iffy backgrounds when it comes to the Russians. trump's campaign employee Page has been approached by the FBI in the past and told point blank he was meeting with sketchy Russians and if he continued he would be investigated. Page ignored them and continued to meet with the Russians, which gave cause to the first FISA warrant being granted. The dossier had little to do with it.
Later, Papa D brags to an Australian diplomat that the trump campaign has gotten dirt on Hillary from the Russians....
Thus starts the witch hunt.