One of the debates surrounding the F.B.I.’s use of information from the Steele dossier in the application is whether it was all crucial to meeting the standard for eavesdropping on Mr. Page’s phone calls and emails.
Asked whether he would have signed off on submitting the application if it did not contain that allegation, James A. Baker, who was the general counsel of the F.B.I. when it first sought permission to wiretap Mr. Page, called the allegation about Mr. Page’s visit to Moscow in 2016 “an important” part of the factual case for surveillance.
“I am not going to sit here and say that there wouldn’t have been probable cause or that there would have been probable cause without the dossier,” Mr. Baker told lawmakers in the fall who were scrutinizing law enforcement officials’ actions during the 2016 election, according to a transcript of his testimony released on Tuesday.
But, he also said, “there were other things in that application that to me were alarming, as well.”
Another F.B.I. lawyer involved in obtaining the warrant, Sally Moyer, told the same committees in October that it was “a close call” but “I think we would have gotten there on probable cause even without the Steele reporting,” a transcript of her testimony showed.
In publicly released documents, the F.B.I. said it had decided to end its relationship with Mr. Steele in November 2016 after he spoke to the news media about his work for the F.B.I. after bureau officials had asked him not to do so.
The inspector general is also scrutinizing another early source of information for the Russia investigation, the people said: Mr. Horowitz’s investigators have been asking questions about the role of Stefan A. Halper, another F.B.I. informant, and his prior work for the bureau.
Agents involved in the Russia investigation asked Mr. Halper, an American academic who teaches in Britain, to gather information on Mr. Page and George Papadopoulos, another former Trump campaign foreign policy adviser.