"We recognize we have employees with political opinions. It's our responsibility to make sure those opinions do not influence their actions,'' Rosenstein said. "I believe that Director Mueller understands that, and he is running his office appropriately."
Rosenstein also said he and Mueller talked about what his office was allowed to investigate and what it was not, though he declined to answer directly whether he had granted Mueller permission to expand his mandate.
"It's a clarification in most cases," Rosenstein said. Asked later whether Trump — who has in the past expressed concern about the probe's scope — had ever talked with him about removing Mueller, Rosenstein responded, "I am not going to be discussing my communications with the president, but I can tell you that nobody has communicated to me a desire to remove Robert Mueller."
Rosenstein has a supervisory role over Mueller.
The deputy attorney general's appearance, which lasted a little less than five hours, came the morning after text messages between two senior FBI officials that disparaged Trump and expressed fear that he might win were turned over to lawmakers. House Judiciary Committee Chairman Bob Goodlatte (R-Va.) referred to the texts in his opening statement, saying they were "deeply troubling to all citizens who expect a system of blind and equal justice."
"Department of Justice investigations must not be tainted by individuals imposing their own political prejudices," Goodlatte said.
The officials who exchanged the messages — senior FBI agent Peter Strzok and senior FBI lawyer Lisa Page — once worked for Mueller's team and were key players in a prior investigation of former Secretary of State Hillary Clinton's use of a private email server. Mueller is investigating whether the Trump campaign and the Kremlin coordinated to influence the 2016 election and already has charged or negotiated plea deals with four people, including former Trump national security adviser Michael Flynn.
Even before the messages were revealed, some Republicans had accused Mueller's team of harboring inappropriate bias, pointing to political contributions by several members to Clinton or other Democrats. Rep. Steve Chabot (R-Ohio) read each of the donations to Rosenstein Wednesday, asking how he could "with a straight face" say they were impartial.
The texts — which Rosenstein said he and Mueller found out about from the Justice Department's inspector general on July 27 — offered new ammunition. Even Rosenstein conceded, "I agree that the text messages raise concern."
One of the earliest messages, from 2015, shows Strzok calling Sen. Bernie Sanders (Vt.), Clinton's rival for the Democratic nomination, "an idiot like Trump. Figure they cancel each other out.'' On March 4, 2016, Page texted, "God, Trump is a loathsome human," to which Strzok replied, "Yet he may win."
"This is not just political opinions. This is disgusting, unaccountable political bias, and there's just no way this could not affect a person's work," said Rep. Louie Gohmert (R-Tex.), as he read out some of the texts. "Were you aware," he asked Rosenstein, "just how biased Mr. Strzok was?" Rosenstein said he was not.
Rep. Jim Jordan (R-Ohio) read an August 2016 text in which Strzok appeared to refer to a meeting in FBI Deputy Director Andrew McCabe's office and commented, "I want to believe the path you threw out for consideration in Andy's office — that there's no way he gets elected — but I'm afraid we can't take that risk."
"This is unbelievable. This is what a lot of Americans are believing right now, and I certainly do: That the Comey FBI and the Obama Justice Department worked with one campaign to go after the other campaign," Jordan said, referencing James B. Comey, the FBI director whom Trump fired in May.
Said Rep. John Ratcliffe (R-Tex.): "If you set out to create an appearance of bias or prejudice or impropriety or conflict of interest, the only way you could do a better job of doing it would be to pick this team and have them wear their 'I'm with her' T-shirts to work every day." "I'm with her" was a slogan of the Clinton campaign.
Democrats, meanwhile, stood up for Mueller, who is a registered Republican.
Rep. Steve Cohen (D-Tenn.) asked Rosenstein to detail why he had chosen Mueller for the job, and after detailing Mueller's credentials, Rosenstein remarked, "I believe he was an ideal choice for this task."
As Cohen then launched his own defense of Mueller, declaring "Everybody respects this man in this country," Gohmert quickly interjected: "I don't."
Rep. Jerrold Nadler (N.Y.), the top Democrat on the Judiciary Committee, said there was nothing wrong with the officials expressing "private political views via private text messages." Strzok, in particular, "did not say anything about Donald Trump that the majority of Americans weren't also thinking at the same time," he said.
Strzok was removed from Mueller's team in late July when his bosses found out about the texts. Page left two weeks earlier for what officials have said were unrelated reasons. Rosenstein said Mueller had taken appropriate action in taking Strzok off the team.
Republicans also have long complained about the Clinton investigation's conclusion, when Comey recommended that she not be charged even as he criticized her and her aides' use of the private server. Goodlatte said the Strzok-Page texts "prove what we all suspected — high-ranking FBI officials involved in the Clinton investigation were personally invested in the outcome of the election and clearly let their strong political opinions cloud their professional judgment."
Goodlatte has called on Attorney General Jeff Sessions to appoint a second special counsel to investigate a host of Clinton-related matters, and Sessions indicated in a response last month that he had directed senior prosecutors to explore some of the topics and report back to him. Nadler said that request was "grossly misguided."
Sessions has recused himself from the case because of his work on the Trump campaign.
The Justice Department Inspector General's Office has said its investigators are looking into the handling of the Clinton email investigation, as well as the texts between Strzok and Page. Rosenstein said he was hopeful the inspector general would conclude his investigation "in the next couple months," adding, "When we get those results, we'll take appropriate action."