Washington • President Donald Trump on Wednesday named Richard Grenell, the ambassador to Germany who quickly antagonized the establishment after arriving in Berlin in 2018, to be the acting director of national intelligence overseeing the nation’s 17 spy agencies.

By choosing Grenell, who has little experience in intelligence or in running a large bureaucracy, the president signaled that he wants a trusted, aggressive leader atop an intelligence community that he has long viewed with suspicion and at times gone to war against.

As ambassador, Grenell made public statements that some German officials took as expressing opposition to the government there, an extraordinary intervention into domestic affairs that diplomats typically avoid. He attacked what he called “failed” open-border policies in Germany, which has resettled hundreds of thousands of Syrian refugees, and criticized Berlin’s stances on Iran, military spending and Chinese investment in global telephone networks. He also expressed an eagerness to empower conservatives throughout Europe.

“I absolutely want to empower other conservatives throughout Europe, other leaders,” Grenell told Breitbart, a far-right website, in an interview shortly after his arrival in Germany. “I think there is a groundswell of conservative policies that are taking hold because of the failed policies of the left.”

While intelligence directors have tried to serve as neutral arbiters of facts, Grenell’s experience as an ideological advocate prompted some former officials to express concern that he could color the intelligence he presents to Trump rather than present an objective assessment.

“This is a job requiring leadership, management, substance and secrecy,” said John Sipher, a former CIA officer. “He doesn’t have the kind of background and experience we would expect for such a critical position.”

Grenell is expected to keep his current ambassadorship as long as he is acting intelligence director, one administration official said. Grenell did not respond to a request for comment.

His bare-knuckled approach clearly resonates with the president and his inner circle. Last spring, shortly before the now-infamous removal of the U.S. ambassador to Ukraine, Marie L. Yovanovitch, the president’s oldest son, Donald Trump Jr., invoked Grenell in a tweet about conservative discontent with Yovanovitch. “We need more @RichardGrenell’s and less of these jokers as ambassadors,” the younger Trump wrote.

Grenell, who has pushed to advance gay rights in his current post, is also thought to be the first openly gay Cabinet member.

Republican senators had privately pushed the administration to nominate a national security professional for the post, and advisers made clear that the president was not nominating Grenell for the permanent job. Trump has installed acting leaders in other top government vacancies, giving him freedom to maneuver around the demands of Senate confirmation.

By law, the current acting director of national intelligence, Joseph Maguire, has to give up his temporary role before March 12. Grenell is expected to begin his new job Thursday.

Maguire has served as acting director of national intelligence since the resignation last summer of Dan Coats, a former Republican senator from Indiana.

Grenell would be the latest in a line of intelligence directors who have had varied policy experience including diplomatic or military backgrounds rather than stints in the intelligence world. But Grenell is also an acerbic combatant who throws regular punches at “fake news” reporters and Trump’s opponents online.

Last month, he angrily demanded The Washington Post retract a report, which he insisted was based on fabricated sources, that Trump had threatened to impose auto tariffs on European cars if European leaders did not adopt a tougher line on Iran’s nuclear program. The next day, Germany’s defense minister publicly confirmed the report.

Grenell honed his combative style when he worked as a spokesman at the United Nations for former ambassador John Bolton. Often to the surprise — and sometimes the horror — of the State Department’s more staid communications officials who worked for Secretary of State Condoleezza Rice, Grenell would take on reporters and argue long into the night about stories appearing in major newspapers and on television.

In recent days, after Attorney General William Barr said in an interview that Trump’s tweets made his job more difficult, Grenell appeared on Fox News to counter that view. “It makes my job so much easier,” Grenell said, offering the example of Trump’s pressure on NATO allies to spend more on defense.

In a country where former President Barack Obama is still widely popular, Grenell’s style put off other officials and ultimately isolated him, the German publication Der Spiegel reported last year. “The powerful avoid him,” the newsmagazine wrote. “Doors have been shut.”

Much of Grenell’s criticism has been directed at German military spending, its decision to stand behind the nuclear deal with Iran, and its wavering on the American demand to ban Huawei, the Chinese telecommunications giant, from building next-generation mobile networks.

He has also had successes, including getting Germany to agree to take American liquefied natural gas and to pull the landing rights of an Iranian airline. A number of German companies have pulled out of Iran, warned by Grenell that they could run afoul of U.S. sanctions if they did business with Tehran.

And while German military spending has continued to rise during the Trump administration, the government in Berlin has ratcheted back its goals for increasing spending.

While most of the previous directors of national intelligence have tried to take a nonpartisan tone, Trump has looked askance at officials who have tried to remain neutral. He has increasingly looked to people for positions who he believes share his views.

“Grenell, from the beginning, was an ultraright-wing sniper on social media,” said Douglas H. Wise, a former senior intelligence official. “He is certainly in line with the Trump agenda.”

Intelligence professionals reacted with surprise, and some with disappointment, questioning Grenell’s experience and temperament. The appointment demonstrated that Trump little understands or values the intelligence community, said Nicholas J. Rasmussen, former head of the National Counterterrorism Center.

“Personal loyalty is prized above relevant experience and demonstrated competence,” said Rasmussen, now acting executive director of the McCain Institute. “Professionalism and integrity are devalued. The signal this sends to our career national security and intelligence professionals is unmistakable.”

Sen. Mark Warner, D-Va., vice chairman of the Senate Intelligence Committee, criticized Trump for appointing another acting director, rather than choosing an official nominee, “apparently in an effort to side step the Senate’s constitutional authority.”

While it has never been clear how Trump viewed Maguire, there is little doubt that the president would prefer a partisan fighter in the post. Maguire, a retired admiral, became acting director in August just as a whistleblower inside the CIA filed a complaint about Trump’s dealings with Ukraine.

Since even before the acquittal of Trump in the Senate impeachment trial, the president has been pushing to remove officials seen as disloyal to or undermining of the president or holding views contrary to the White House, looking for replacements who are more likely to follow the president’s wishes.

Trump has at times disparaged U.S. intelligence agencies because he did not agree with their findings, perhaps chiefly the conclusion that Russia interfered with the 2016 presidential election to help him win. The president told his intelligence chiefs to “go back to school” after a congressional briefing during which they offered assessments on Iran and North Korea at odds with his policy initiatives.

Anxious to avoid a repeat, Maguire’s aides initially pushed for this year’s public hearing to be canceled, a request that lawmakers have rejected.

Tensions between the White House and intelligence agencies only grew during the impeachment inquiry. Maguire initially blocked the whistleblower complaint from being forwarded to Congress, following the guidance of administration lawyers. But he eventually helped broker the agreement to provide the complaint to Congress’ intelligence committees, allowing the impeachment inquiry to gain steam.

When Coats announced his resignation in July, Trump initially nominated an ally, Rep. John Ratcliffe, R-Texas, to be the next top intelligence chief, a job considered to be among the most nonpartisan in Washington. But Trump quickly dropped those plans after pushback from Democrats and some key Republicans who worried Ratcliffe’s loyalty to the president and lack of intelligence experience would make him nearly impossible to confirm. There were also concerns that Ratcliffe exaggerated his résumé.

After Ratcliffe was dropped from consideration, Trump promised to announce a new nominee soon. But the list of people with the requisite experience who have not been critical of the president is slim.

The administration considered, and discarded, a number of potential nominees including Pete Hoekstra, the U.S.ambassador to the Netherlands and a former Republican chairman of the House Intelligence Committee, and Rep. Chris Stewart, R-Utah, a committee member.