I don't post often these days, but as "the memo" appears to have landed, I thought now might be a good time to summarise what's known about one of the other, non Christopher Steel dossier, major sources was for FBI and CIA information about Russian hackers infiltrating US government computer systems and targeting Clinton: the Dutch government.
The source of my information is a series of articles published over the past 2 weeks by the Volkskrant. I believe the Volkskrant has the highest circulation of any national newspaper in the Netherlands, it is the flagship of a very large media organisation—a media organisation, by the way, that is generally seen to be moderate or right-of-centre (not insane right-wing like its rival De Telegraaf, which also also has a media empire). The Volkskrant is well-connected with the current moderate-right Rutte government and has clearly developed some very well-informed sources.
So here's the run-down (warning: though I am technically fluent, my Dutch is not perfect and I may have missed a nuance somewhere on the way. That said, Dutch generally doesn't do 'nuance' so I think I've not missed much!) The AIVD (Dutch secret service), the MIVD (Dutch military secret service) and the Dutch high-tech fraud squad have both been very busy in recent years tracking the activities of Russian hackers. This ramped up in 2014, when an airplane carrying many Dutch citizens was shot down over the Ukraine, presumably by Russian-backed forces. So it's no surprise that 2014 was a key year in this long-running investigation, and the AIVD got lucky—they got inside the network of a group of Moscow hackers called '’Cozy Bear" (I don't know if this is a translation of the group's actual Russian name or a code name), which had infiltrated the computer systems of the US Department of State, the Democratic Party and the White House.
They did a pretty thorough job — not only was the AIVD/MIVD able to observe the computer activities of the group and at least one other associated hacker group as they tried various methods of accessing information in the DoS and other US government systems, and how they traded this information with actors in and around the Russian government, they got photos of people walking in and out of the building where they operated and compared these with photos and background information about known Russian hackers and secret service operatives/spies. The AIVD and MIVD have human spies as well as their cyber-activities, and this information has been correlated to create a bigger picture about the players, their goals, etc. This information has been discussed in secret meetings with top Dutch government ministers (the fact they happened isn't secret, but the contents are.)
It very quickly became evident to the AIVD/MIVD that the hacker group and its government handlers were obviously trying to '’undermine democracy'’ in an important ally, and they began to work hand in hand with the US secret services, including the FBI and presumably the CIA. The hackers were also trying to hack the Dutch government—obviously, that's why the AIVD/MIVD was interested in the first place—and this is believed to have been successfully blocked, although there are many concerns currently about hacking of elections, influence within political parties (we have dozens, some of them dodgy, and parties don't have to reveal the source of their funds), and security of government data in general. This co-operation with the US was coming along quite nicely until the election of the current inhabitant of the White House, although there is a general view that the Democratic Party and the FBI did not take the threat seriously enough and made some crucial screw-ups.
Because it's important for establishing that the Steele dossier was the not the actual root cause of the FBI investigation, I'll translate these sentences directly:
De Nederlandse inlichtingendiensten werkten de afgelopen jaren nauw samen met hun Amerikaanse collega's en wisten op cruciale momenten informatie door te spelen over cyberaanvallen van de Russen. De relatie tussen de diensten van beide landen was goed totdat Trump tot president was gekozen en het Witte Huis aanvankelijk de berichtgeving over Russische inmenging afdeed als nepnieuws.
Translation: The Dutch secret service worked together with their American colleagues during the ensuing period [starting from summer 2014, remember], and shared information at crucial moments about Russian cyber-attacks. The relationship between the two countries was good, until Trump was elected and the White House initially tagged the messages about Russian meddling as 'fake news'."
So—even if the Steele dossier had never existed, the FBI knew about Russian hacking aimed at the US government, the Democratic Party, and Hilary Clinton (as Secretary of State and potential candidate) long before it was a factor. Indeed, although Mr Steel is well-connected, I would imagine that the FBI was much more alarmed about information received from an actual live investigation by the secret service of a key European ally.