Rod Rosenstein, Key Figure in Russia Inquiry, Defends Mueller Appointment

“I do not consider the investigation to be corrupt, Senator, but I certainly understand the president’s frustration given the outcome,” Mr. Rosenstein said to Senator Richard J. Durbin, Democrat of Illinois, noting that Mr. Mueller did not charge any of Mr. Trump’s associates with conspiring with Russia’s interference operation.

Lawmakers clash over whether investigating Trump associates was justified.

Republican and Democratic senators used the questioning of Mr. Rosenstein as a proxy to argue about whether the investigation was justified, given that Mr. Mueller ultimately did not find evidence to charge any Trump campaign associates with conspiring with the Russians.

Mr. Graham pushed Mr. Rosenstein to explain why he appointed Mr. Mueller in May 2017 and then signed a memo clarifying the scope of the special counsel investigation that August that included scrutinizing whether campaign associates were working with Russia — pointing out that investigators had found no proof that they were. Mr. Rosenstein repeatedly tried to explain that the purpose of investigations is to find out whether there is proof.

Eventually, Mr. Graham declared, “the point is, the whole concept that the campaign was colluding with the Russians, there was no ‘there’ there in August 2017. Do you agree with that or not?” Mr. Rosenstein said he agreed.

Later, Senator Patrick Leahy, Democrat of Vermont, pushed back. He asked questions emphasizing that the fundamental matter being investigated was the scope of the covert Russian election interference operation and what to make of links to the Trump campaign, including Mr. Trump’s public comments in 2016 asking Russia to hack Hillary Clinton’s emails.

“We do have then the unanimous assessment within the intelligence community, and the Republicans and Democrats on the Senate Intelligence Committee: Russia interfered in our election,” Mr. Leahy said. “Now, I believe this was interference that the Trump campaign welcomed and attempted to exploit — ‘Mr. Putin, are you listening’ and so on. Any argument suggesting that the Russia investigation should have never occurred, and the American people should be in the dark about Russia’s interference in our election in 2016, I find that deeply troubling.”

Under intense Republican criticism, Rosenstein defended his role in a plagued set of wiretap applications.

In December, the Justice Department’s independent inspector general, Michael E. Horowitz, released a damning report about errors and omissions by the F.B.I. in applications to obtain a national security wiretap order targeting Carter Page, a former Trump campaign adviser, in October 2016, as well as three renewal orders in 2017.