WASHINGTON — President Trump said on Friday that he would nominate William P. Barr, a skeptic of the Russia investigation who served as attorney general in the first Bush administration a quarter century ago, to return as head of the Justice Department.
Mr. Barr, 68, would become the nation’s top law enforcement official as Mr. Trump and his associates are under investigation by the special counsel, Robert S. Mueller III, for whether they conspired with the Russian government to interfere in the 2016 election and help elect Mr. Trump. Mr. Barr would oversee the inquiry as key aspects of it are coming to a close.
Known for his expansive vision of executive power, Mr. Barr has criticized Mr. Mueller for hiring too many prosecutors who donated to Democrats and has cast doubt on whether Trump campaign associates conspired with Russians. Mr. Barr has also defended Mr. Trump’s calls for a new criminal investigation into his defeated 2016 opponent, Hillary Clinton, including over a uranium mining deal the Obama administration approved when she was secretary of state.
His nomination comes at a time of more than usual turbulence in the Trump White House, where John F. Kelly, the president’s second chief of staff, is expected to end his stormy 16-month tenure as early as this weekend. Nick Ayers, the vice president’s chief of staff, is seen as a leading candidate to succeed Mr. Kelly, although Mr. Ayers has enemies on the White House staff and is not universally beloved by Republicans.
Mr. Trump also announced on Friday that Heather Nauert, the State Department spokeswoman, would be his nominee for the next ambassador to the United Nations. Ms. Nauert, who until last year was a Fox News personality and has no prior policymaking experience, would replace Nikki R. Haley, the former governor of South Carolina.
Mr. Trump’s choice of Mr. Barr, an experienced corporate lawyer from the Republican legal establishment, was greeted with a measure of relief inside the Justice Department. Matthew G. Whitaker, the acting attorney general whom Mr. Trump installed last month after he fired Jeff Sessions from the post, has been a particularly outspoken critic of the Mueller investigation and has separately come under scrutiny for his role with a company that a federal judge shut down for defrauding its customers.
Mr. Barr is likely to be swiftly confirmed by the Republican-controlled Senate.
As attorney general, the job he held from 1991 to 1993, Mr. Barr would wield tremendous influence over immigration policy, civil rights, criminal law, environmental enforcement and national security matters. But looming over all would be managing Mr. Mueller.
Senator Chuck Schumer of New York, the Democratic leader, said on Friday that Democrats would rigorously scrutinize Mr. Barr during confirmation hearings on a range of issues, but he put a central focus on the Russia investigation.
“Mr. Barr must commit — at a minimum — under oath before the Senate to two important things: first, that the special counsel’s investigation will proceed unimpeded, and second, that the special counsel’s final report will be made available to Congress and the public immediately upon completion,” Mr. Schumer said.
Mr. Barr, the son of an educator who was dean of Columbia University’s engineering school, was raised in New York, where he attended Horace Mann. He graduated from Columbia with a master’s degree in Chinese studies in 1973, and that year went to work as an officer at the Central Intelligence Agency. When Congress began major oversight investigations into intelligence abuses, he worked in the C.I.A.’s legislative counsel’s office and attended law school at night at George Washington University.
He clerked for a year on the Court of Appeals for the District of Columbia for Judge Malcolm R. Wilkey, a conservative who had notably dissented a few years earlier from a ruling that President Richard M. Nixon had to turn over tape recordings. Judge Wilkey advanced a stronger view of presidential executive privilege powers than the court majority.
Mr. Barr — who has never been a prosecutor, an unusual background for a once and likely future attorney general — then went to work in private practice while becoming active in Republican politics. He later joined the Reagan White House as a domestic policy official, where he worked on deregulatory issues with C. Boyden Gray, the counsel to Vice President George Bush.
In 1989, after Mr. Bush became president and Mr. Gray became his White House counsel, Mr. Gray recruited Mr. Barr to become the head of the Justice Department’s powerful Office of Legal Counsel.
In that role, Mr. Barr advanced a strong view of executive power. He told Mr. Bush, for example, that he could deploy troops to Panama, Iraq and Somalia without congressional approval. He also urged top lawyers at departments across the executive branch to be vigilant about congressional encroachments on executive power.
“We set up some things because of Boyden’s and my own interest in the powers of the presidency — and President Bush’s, too — because I think Bush felt that the powers of the presidency had been severely eroded since Watergate and the tactics of the Hill Democrats over an extended period of time when they were in power,” Mr. Barr recalled in a 2001 oral history.
In an interview on Friday, Mr. Gray called Mr. Barr “very businesslike and straightforward, a very good lawyer.” But Mr. Gray also cautioned against making too much of Mr. Barr’s writings about executive power at the time as potential foreshadowing of what he might do in the Trump administration.
Mr. Gray argued that 1989 was a particular moment in history when he and Mr. Barr believed there needed to be a rebalancing because in their view Congress had overreached in curbing executive power after the Watergate and Iran-contra scandals.
As Mr. Bush’s term progressed, he elevated Mr. Barr to deputy attorney general and then to the top job in the department. Among other things, that put Mr. Barr in charge of the nation’s immigration enforcement agencies, and he pushed to take a harder line.
As he recalled in the oral history, Mr. Barr waged bureaucratic battles to station immigration officers at major foreign airports to screen passengers bound for the United States before they boarded planes, hoping to curtail people’s ability to claim asylum — a process that he, like Mr. Trump, has criticized as flawed and subject to abuse.
“People would get on the airplane, they’d come to the United States, and then they’d claim asylum as soon as the airplane touched down,” he said. “Under our laws, we have this very robust process that they have to go through. They’d be put out on parole pending their asylum hearing, and then they’d disappear.”
After a 1991 coup in Haiti, Mr. Barr pushed to detain at the American naval base at Guantánamo Bay, Cuba, fleeing Haitians who had been intercepted at sea en route to Florida. Mr. Barr wanted to screen out those who were not deemed to be legitimate political refugees or who were infected with the virus that causes AIDS. That led to tensions with military leaders.
“Their position was, ‘Guantánamo is a military base, and why were all these people here, the H.I.V. people, all these other people? How long are you going to be on our property with this unseemly business?’” Mr. Barr recalled in the oral history. “I’d say, ‘Until it’s over. But we’re not bringing these people into the United States.’”
Mr. Barr’s emphasis on keeping undocumented migrants out of the country dovetails with the approach of Mr. Sessions, who was a United States attorney in Alabama when Mr. Barr was attorney general. Mr. Sessions had hung Mr. Barr’s portrait in his conference room as a tribute when Mr. Sessions became attorney general in 2017.
Both men also supported the use of tough-on-crime policies to combat rising drug use during the first Bush administration.
In December 1992, after Bill Clinton defeated Mr. Bush for the presidency, the Justice Department came under pressure to address allegations that Bush administration officials had improperly searched Mr. Clinton’s passport file in search of campaign dirt.
Mr. Barr decided to trigger the appointment of an independent counsel to investigate. The resulting inquiry lasted three years but led to no charges, and his decision embittered his former colleagues who came under scrutiny.
In a 2015 interview, Mr. Barr insisted that he had made the right decision under the law. Still, he also made clear that he believes special prosecutors need to be subjected to rigorous supervision to avoid “injustice.”
Giving a prosecutor “just a single mission” creates “a built-in bias to find a basis for indictment,” Mr. Barr said then. “Every subject who’s subject to that, it’s very difficult to avoid finding something in the course of an investigation to indict them for.”
After leaving the Justice Department in 1993, Mr. Barr became the top lawyer for GTE, the company that became Verizon Communications.
After retiring from Verizon in 2008, he joined the law firm Kirkland & Ellis.
During his earlier stint in the Justice Department, Mr. Barr worked with Mr. Mueller, then head of the criminal division, and with Pat Cipollone, Mr. Trump’s incoming White House counsel.
When the White House asked Mr. Barr if he would consider the job, he declined, according to a person familiar with the negotiations. But lawyers who work with the White House appealed to Mr. Barr’s sense of service, saying he could calm tensions with the White House and restore morale in the department.
At a law enforcement conference in Kansas City, Mo., on Friday, Mr. Whitaker called Mr. Barr “supremely qualified.” Mr. Trump, at the same event, called Mr. Barr an “outstanding man,” noting that he received a “unanimous confirmation” in 1991.
“During his tenure, he demonstrated an unwavering adherence to the rule of law, which the people in this room like to hear,” Mr. Trump said. “He deserves overwhelming bipartisan support. I suspect he’ll probably get it.”
Reporting was contributed by Peter Baker and Katie Benner from Washington, Maggie Haberman from New York and Annie Karni from Kansas City, Mo.
Follow Charlie Savage on Twitter: @charlie_savage.