Sen. Lindsey Graham, the chairman of the Senate Judiciary Committee, on Sunday revealed the questions his panel wants answered about why the FBI launched an investigation into former Trump campaign adviser Carter Page.

“Now, I want to know, what did McCabe and Comey know, when did they know that the dossier was unreliable?” Graham (R-SC) said in an interview on Fox News’ “Sunday Morning Futures.”

He was referring to former FBI Director James Comey, former acting Director Andrew McCabe and a dossier compiled by one-time British spy Christopher Steele.

Justice Department Inspector General Michael Horowitz in December released a report on the Foreign Intelligence Surveillance Act that was used by the FBI to monitor Page — an action that led to the launch of the agency’s investigation into Russian meddling.

Horowitz’s report showed that the FBI and the Justice Department heavily relied on Steele’s dossier, which contained a series of unsubstantiated claims about President Trump and Russia.

Graham, noting that a primary source for Steele told the FBI that the information in the dossier wasn’t credible, expressed skepticism that the allegations failed to reach the highest levels of the FBI.

“I find it hard to believe that that did not work its way up to Comey and McCabe,” Graham said.

He went on to say he wants to begin the probe by having the four people who met with Steele’s source to testify before his committee.

Graham also said he’s curious to know who else knew about the dossier not being credible, including former acting Attorney General Rod Rosenstein.

“Did Rosenstein know that the dossier had been debunked by the time he signed the warrant? How could he not know?” Graham asked.

Rosenstein supervised then-special counsel Robert Mueller’s investigation into Russia after then-Attorney General Jeff Sessions recused himself from the probe.

Following Trump’s firing of Comey in May 2017, Rosenstein appointed Mueller special counsel.

“Here’s my question to Rosenstein: if you knew then what you know now, that it was a bunch of garbage, would you have appointed Mueller?” Graham said.

He didn’t specify when he would call the witnesses to testify as the committee begins hearings this week.