The Steele dossier is the subject of investigations into possible collusion between Trump and Russia.
Simpson’s research firm is at the heart of multiple allegations of ties between President Donald Trump and Russia.
Glenn Simpson, whose firm compiled an infamous dossier on Donald Trump, spent more than 10 hours talking with Senate investigators.
Christopher Steele has gone into hiding since his explosive allegations about President Donald Trump were made public.
A newcomer to politics, businessman Trump has been at odds with U.S. spy agencies for months, disputing their conclusions that Russia used hacking and other tactics.