The Nunes memo (of #ReleasetheMemo fame) suggested it in a more general way. The Grassley\Graham memo (memo 2 or in the less redacted version, memo 2.1) states it more definitively.
The documents we have reviewed show that the FBI took important investigative steps largely based on Mr. Steele’s information–and relying heavily on his credibility. Specifically, on October 21, 2016, the FBI filed its first warrant application under FISA for Carter Page... The bulk of the application consists of allegations against Page that were disclosed to the FBI by Mr. Steele and are also outlined in the Steele dossier. The application appears to contain no additional information corroborating the dossier allegations against Mr. Page, although it does cite to a news article that appears to be sourced to Mr. Steele’s dossier as well.
That's the Yahoo News/Isikoff article whose provenance the FISA court appears to have been deceived about.
So the FISA application really originated with Clinton opposition research. We've been told by the apologists that there just has to be "something" more. Memo 2.1 makes it clear that there was hardly anything else except unverified opposition research.
The case was built on Steele. And even after it had to dump him, it still kept relying on him.
In footnote 9 of its January 2017 application to renew the FISA warrant for Mr. Page, the FBI again addressed Mr. Steele’s credibility. At that time, the FBI noted that it had suspended its relationship with Mr. Steele in October 2016 because of Steele’s “unauthorized disclosure of information to the press.”
The FBI relayed that Steele had been bothered by the FBI’s notification to Congress in October 2016 and the reopening of the Clinton investigation, and as a result “[Steele] independently and against the prior admonishment from the FBI to speak only with the FBI on this matter, released the reporting discussed herein [dossier allegations against Page] to an identified news organization.” However the FBI continued to cite Mr. Steele’s past work as evidence of his reliability, and stated that “the incident that led to the FBI suspending its relationship with [Mr. Steele] occurred after [Mr. Steele] provided” the FBI with the dossier information described in the application...
… In defending Mr. Steele’s credibility to the FISC, the FBI had posited an innocuous explanation for the September 23 article, based on the assumption that Mr. Steele had told the FBI the truth about his press contacts. The FBI then vouched for him twice more, using the same rationale, in subsequent renewal applications filed with the Foreign Intelligence Surveillance Court in April and June 2017.
You know that guy we can't trust anymore, who is obsessed with defeating Trump and electing Hillary, please go on trusting everything he told us. Because he only stopped being credible once he gave us the information.