The US Senate on Thursday confirmed William Barr as the country’s next attorney general, putting the veteran Republican lawyer in charge of Special Counsel Robert Mueller’s probe of any ties between President Donald Trump‘s campaign and Russia.

The Republican-controlled Senate voted 54 to 45, largely along party lines. He could be sworn in before the end of the week.

Previously attorney general from 1991 to 1993 under President George HW Bush, Barr has won praise from politicians in both parties for his expertise and grasp of the workings of the Justice Department, which will head.

He will be the third man in barely two years to occupy the attorney general post, replacing acting Attorney General Matthew Whitaker, who replaced Attorney General Jeff Sessions. Trump removed Sessions last November after criticising him repeatedly.

Mueller investigation questions

Mueller is investigating meddling by Russia in the 2016 US presidential election and whether Moscow colluded with Trump’s campaign to try to tilt the election in Trump’s direction, as well as possible obstruction of justice. Trump has denied any collusion and has repeatedly called the investigation a “witch-hunt”. and The Kremlin has also denied any meddling.

Before being nominated, Barr wrote a 19-page legal memo, which he shared with Trump’s legal team and Justice Department officials. It called Mueller’s probe “fatally flawed”.

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Barr has said he will not let himself be bullied by Trump and will protect the integrity of Mueller’s investigation and make public as many of its findings as he can.

Barr has not promised to release Mueller’s report in its entirety. He has warned he may not be allowed to reveal the identities of people who escape prosecution. That stance troubles many Democrats, who say Barr’s expansive views of executive power might lead him to suppress parts of the report.

Despite Democrats’ opposition, many were still anxious to have Barr installed quickly so that he can replace Whitaker, whose tenure has been fraught with controversy since Trump installed him in November.

Critics have alleged Whitaker’s appointment was unlawful. Democrats fear Trump installed Whitaker to undermine Mueller’s probe because Whitaker had criticized it when he was a conservative pundit.

Barr is widely expected to back many of Trump’s tough immigration policies. He will also be under the microscope for how he implements a new law that eases prison sentences for non-violent criminals, after he advocated for the opposite, tough-on-crime approach for decades.