How soon did the FBI know about the opposition research report written by a former British intelligence official for political opponents of President Donald Trump?

That question is one of several asked by Senate Judiciary Committee Chairman Charles Grassley in a letter sent to FBI director James Comey in a letter sent earlier this month after the Washington Post reported that the law enforcement agency entered into negotiations with Christopher Steele, a former agent for the U.K.’s foreign intelligence service, MI6.

Steele was commissioned by an opposition research firm to dig into allegations that the Russian government had a substantial amount of compromising information on Trump by Republican opponents of Trump during his effort to win the GOP presidential nomination. After he became the party nominee, a backer of the 2016 Democratic nominee, Hillary Clinton, continued to pay for Steele’s investigations.

In October, just a few weeks before the election, the FBI agreed to fund Steele’s investigations even as it remained unsure about their veracity. No payments were ever exchanged, however, after Steele’s work became public knowledge and the dossier was attacked for repeating unsubstantiated and false claims.

“The idea that the FBI and associates of the Clinton campaign would pay Mr. Steele to investigate the Republican nominee for president in the run-up to the election raises further questions about the FBI’s independence from politics,” Grassley wrote in a March 6 letter to Comey.

The Nebraska senator asked the FBI to provide detailed documentation about its contacts with Steele as well as information about the agency’s policies about using investigatory work commissioned by opposition research companies. He sent a similar one to Fusion GPS, the firm which had hired Steele.

The FBI has come under intense criticism from both parties regarding its activities during the 2016 presidential election. Democrats have criticized Comey for departing from agency protocol in October by announcing that the FBI had re-opened its investigation into Hillary Clinton’s private email server. Normally, the agency does not comment on its activities.

Democrats have criticized Comey for not similarly informing the public and members of Congress that it had also opened an investigation into the possible connections between associates of Donald Trump and the government of Russia.