Special counsel Robert Mueller’s investigation into Russian interference in the 2016 election and whether the Trump campaign colluded with the Kremlin is “appropriate and independent,” said Deputy Attorney General Rod Rosenstein in a new report.

Rosenstein has attracted the ire of some GOP lawmakers for his role overseeing Mueller’s probe, which critics say has lasted long enough and is biased against Trump. Trump has also labeled the investigation a “witch hunt” and routinely condemns the probe.

“People are entitled to be frustrated, I can accept that,” Rosenstein said, per the Wall Street Journal. “But at the end of the day, the public will have confidence that the cases we brought were warranted by the evidence and that it was an appropriate use of resources.”

Media reports have previously circulated claiming that Trump was planning to oust Rosenstein, but Trump said last week that he doesn’t plan to fire Rosenstein and that the two “actually have a good relationship.”

Meanwhile, Republicans such as Rep. Mark Meadows, R-N.C., have raised the possibility of impeaching Rosenstein, most recently after it was reported Rosenstein talked about secretly recording the president and invoking the 25th Amendment to remove Trump from office.

Rosenstein has denied the allegations and refused to discuss the report or how it has influenced his relationship with Trump.

“The president knows that I am prepared to do this job as long as he wants me to do this job,” said Rosenstein. “You serve at the pleasure of the president, and there’s never been any ambiguity about that in my mind.”

While Rosenstein declined to comment on when the Russia probe would conclude, Bloomberg News reported Wednesday that Mueller is poised to share key findings of the investigation with the Justice Department after the 2018 midterm elections.

“I committed I would ensure the investigation was appropriate and independent and reached the right result, whatever it may be,” said Rosenstein. “I believe I have been faithful to that.”