Officials announced on Feb. 28 that Hope Hicks will resign. She had been White House communications director since Sept. 2017. (The Washington Post)

Hope Hicks, the White House communications director and one of President Trump’s longest-serving and closest advisers, abruptly announced Wednesday that she plans to resign — sending a jolt through a West Wing besieged by internal tumult and the intensifying Russia investigation.

Hicks, 29, began working for Trump before he announced his candidacy and has been a trusted confidante for three years, shaping his image, managing his moods and counseling him on nearly all matters, from the substantive to the trivial.

A political neophyte who was fiercely loyal to her boss, Hicks exerted extraordinary influence in Washington and was treated by the president almost as a surrogate daughter. She had been widely expected to remain working for Trump until the end of his presidency — and possibly even beyond.

But her special relationship with the president has ensnared Hicks in special counsel Robert S. Mueller III’s wide-ranging investigation of Russian interference in the 2016 election and of possible obstruction of justice by the president. She has come under scrutiny for, among other things, her role aboard Air Force One last year helping the president draft a misleading statement about his son Donald Trump Jr.’s 2016 meeting with Russians.

Hicks has been interviewed by Mueller’s team, and on Tuesday she testified for nine hours before the House Intelligence Committee as part of its separate Russia investigation. She admitted to telling what one person familiar with her testimony characterized as white lies. Hicks told the ­committee that she sometimes stretched the truth on ­minor matters at Trump’s direction but that she had never lied about anything relevant to the investigation, ­according to this person, who spoke on the condition of anonymity because the testimony was confidential.

President Trump set a record for White House staff turnover in the first year. Here's an ongoing list of White House staff, Cabinet members, and federal appointees who quit or were fired under Trump. (Joyce Koh/Washington Post)

White House officials insisted that Hicks’s decision to leave the administration was in the works for several weeks and had nothing to do with the Russia probe or her appearance on Capitol Hill this week. They said Hicks was burned out by three years working in the whirlwind of the Trump orbit, with crises occurring by the day and sometimes by the hour, and she told the president she was ready to pursue opportunities in the private sector.

“There are no words to adequately express my gratitude to President Trump,” Hicks said in a statement. “I wish the President and his administration the very best as he continues to lead our country.”

In his own statement, Trump said, “Hope is outstanding and has done great work for the last three years. She is as smart and thoughtful as they come, a truly great person. I will miss having her by my side but when she approached me about pursuing other opportunities, I totally understood. I am sure we will work together again in the future.”

Hicks’s exit, which was first reported by the New York Times, comes at an especially fraught and tumultuous time for the administration. Mueller’s investigation is creeping closer to the Oval Office with a guilty plea and cooperation agreement from ­former deputy campaign chairman Rick Gates. And Jared Kushner, the president’s son-in-law and senior adviser, has had his security clearance level downgraded, depriving him of details about the nation’s top secrets.

Hicks is only the latest senior aide to depart. Staff secretary Rob Porter, who oversaw the flow of information to the president, exited earlier in February after both of his ex-wives accused him of domestic abuse. And on Tuesday, Josh Raffel, the deputy communications director who was a go-to crisis manager and worked closely with Hicks, announced that he planned to resign.

Hicks’s resignation leaves Trump — a man who runs the White House like a family business and likes to surround himself with loyalists — increasingly isolated in his own West Wing, which has returned to the chaos and tumult of its earliest days.

“Trump is a lone-wolf president in a sequestered White House,” said Douglas Brinkley, a presidential historian at Rice University. “He doesn’t trust his own agencies. He’s at war with his Justice Department. His son-in-law can’t get a security clearance. Hicks says she told white lies on his behalf and is disappearing. It’s just raining bad news on the president. He’s in a corner and there’s no easy exit.”

Only a few “Trump originals” remain working in the White House, including Kushner; Ivanka Trump, the president’s daughter and senior adviser; and Dan Scavino, a golf caddie turned social media director. First lady Melania Trump is an infrequent presence during the day, and one of the president’s closest friends in the White House, longtime former bodyguard Keith Schiller, left his job as director of Oval Office operations last fall.

Trump was protective of Hicks — whom he sometimes affectionately referred to as “Hopey” — and she was the same of him.

Despite her title as communications director, Hicks functioned more as Trump’s personal public relations agency. Especially in the early months of the presidency, Hicks was a gatekeeper for top reporters, unilaterally whisking her favorite journalists into the Oval Office to mingle with the president.

From her closet-size office just outside Trump’s, Hicks often called reporters to try to shape stories more favorably for her boss and took negative reports about him as a personal affront. She has privately lamented that she believes many people in the outside world — and especially in the news media — do not understand Trump’s true compassion and empathy.

Hicks, who began in the White House as director of strategic communications, steadily assumed more responsibility and was called to stabilize the overall communications operation last summer. She was named communications director, overseeing a staff of dozens, in July when Anthony Scaramucci was fired from the post after just 10 days on the job. He was preceded by Mike Dubke and Sean Spicer. During the transition, Jason Miller was appointed communications director but stepped down before Trump took office.

Unlike other top White House communicators, Hicks carefully avoided being in the news. She talked regularly with reporters in private and coached the president and others about what they should say, but she hardly ever appeared on television as a surrogate.

“When I became Chief of Staff, I quickly realized what so many have learned about Hope — she is strategic, poised and wise beyond her years,” White House Chief of Staff John F. Kelly said in a statement. “She became a trusted adviser and counselor and did a tremendous job overseeing the communications for the President’s agenda including the passage of historic tax reform. She has served her country with great distinction. To say that she will be missed, is an understatement.”

Senior administration officials described Hicks as exhausted by the past several months and, in particular, the Porter situation. She was dating Porter, a relationship first reported by the Daily Mail on Feb. 1, and had news photographers staking out her Washington apartment building. Later in February, both of Porter’s ex-wives accused him of domestic abuse, and Hicks was involved in the White House’s initial defense of him before he departed amid a mounting scandal.

One White House adviser said Hicks had been “deeply shaken” by the news media’s coverage of the relationship. Some colleagues said she told them she was physically exhausted and psychologically drained, hated that her personal life had become a news subject, and at times was seen in tears in the West Wing.

Hicks had been contemplating leaving the White House for several weeks and told friends that she was relieved to finally announce her move and was eager to be able to spend more time with her family in Connecticut, officials said. But Hicks also has made clear to friends that she could see herself working for Trump again — including, potentially, during the 2020 reelection campaign.

Hicks was crying as news of her impending departure rippled through Washington and beyond, one senior official said. Though she had told some key West Wing colleagues of her plans, she had not had an opportunity to brief the whole communications staff until shortly after the Times reported that she was leaving, the official said. She told her staff that Washington had worn on her and that she was ready to flee, another official said.

A former fashion model raised in Greenwich, Conn., Hicks entered Trump’s universe as a public relations consultant to his daughter Ivanka. She then went to work directly for Ivanka Trump’s company, from where she was recruited to join Donald Trump’s presidential campaign in its infancy.

“Hope Hicks is loved & admired by all who know her,” Ivanka Trump tweeted Wednesday. “It’s with a heavy heart, but tremendous gratitude, that I wish her well in her next steps.”

By her own admission, Hicks knew little to nothing about politics. But she had a preternatural ability to manage Trump’s whims and appetites and soothe his mood swings. On the campaign trail, Hicks was more than a press secretary. She was a multitasker, part strategist and part travel buddy, whose tasks included steaming the candidate’s pants before his rallies, often while he was wearing them.

Despite studiously eschewing the spotlight, Hicks increasingly found herself in it. During Trump’s trip to Asia last fall, Hicks was part of the coterie of aides who accompanied the president to a state dinner in Tokyo. Ever the sartorialist, Hicks wore a sleek black tuxedo, complete with a bow-tie.

The next morning, Hicks’s ­visage was beamed around the world.

Josh Dawsey, Carol D. Leonnig and Rosalind S. Helderman contributed to this report.