Senate Judiciary Committee Chairman Chuck Grassley originally subpoenaed Simpson last month after Simpson refused to testify before the committee, but the Iowa Republican dropped the subpoena after Simpson agreed to speak privately with committee staff.
Simpson is the first of three major players in the ongoing Russia probes to speak with judiciary staff. Donald Trump Jr. and former Trump campaign chairman Paul Manafort both cut deals to speak with committee staff in private
as well, but their dates have not been scheduled yet.
Josh Levy, Simpson's attorney, issued a statement following the conclusion of the meeting.
"Mr. Simpson told Congress the truth and cleared the record on many matters of interest to congressional investigators," Levy said.
Grassley, and California Sen. Dianne Feinstein, the panel's top Democrat, have also sought interviews with Trump Jr. and Manafort, following news of their meeting with a Russian lawyer last year looking to repeal Russian sanctions.
Grassley and his committee are nominally investigating Simpson's alleged failure to register as a foreign lobbyist
-- something Simpson's team has vehemently denied. But investigators are also prying into his role in compiling the Russia dossier, which was filled with some stunning but also unsubstantiated allegations, along with some intelligence about alleged meetings between the Trump campaign and Russian operatives
A spokeswoman for Simpson declined comment for this article. However, Simpson's firm, Fusion GPS, rebutted the committee's request for information in a statement last month.
"Let's be clear about what's really happening: the President's political allies are targeting Fusion GPS because the firm was reported to be the first to raise the alarm over (the) Trump campaign's links to Russia," Fusion GPS said in an unsigned statement delivered to the Senate judiciary committee last month.
The Senate intelligence committee has led the bulk of Senate inquiries into the Russian interference in the 2016 election and possible collusion with the Trump campaign. But the Senate judiciary committee has ramped up its own inquiries in recent months, getting access to critical documents that included 20,000 pages of emails from the Trump campaign and the memos that former FBI Director James Comey drafted of his private meetings with Trump, according to the Washington Post