A hard-charging conservative lawyer little known to the public is responsible for executing some of the White House’s most divisive and legally aggressive moves, including the hold on Ukrainian aid now central to President Trump’s impeachment trial.

Mark Paoletta, general counsel at the White House Office of Management and Budget, signed off on the delay of security assistance to Ukraine, overruling the objections of some career staffers at the OMB and the Pentagon. The Government Accountability Office recently determined that the delay was unlawful.

Paoletta’s below-the-radar role in a decision key to Trump’s impeachment is just one example of how he has enabled the White House to stretch the legal limits of the executive branch — forcefully pushing forward the administration’s agenda but sometimes incurring a severe backlash in the process.

Paoletta helped craft the administration’s justification for adding new restrictions to billions in disaster aid to Puerto Rico, blowing past a congressional deadline and ignoring fierce criticisms from the island’s government.

He also provided the legal foundation for Trump’s move to redirect Pentagon money and use it to erect a wall on the border with Mexico. That legal maneuver was opposed by another top White House attorney, according to officials familiar with internal deliberations, and has been criticized by congressional lawmakers in both parties.

Paoletta similarly helped engineer the Trump administration’s maneuvering during last year’s government shutdown to minimize the impact, a move the GAO also said broke federal law.

Internally, Paoletta has battled with other White House attorneys who helped block a push to make him a part of Trump’s defense team for impeachment charges in the Senate, according to officials familiar with that process, although he himself did not push for the position. His approach has also rankled some career staffers at the OMB, with some officials saying it has caused career employees to feel dismissed or even demeaned.

The Washington Post interviewed more than a dozen current and former OMB employees, as well as numerous other White House officials and legal experts, who painted a portrait of Paoletta’s work as the top lawyer at the OMB. Many were granted anonymity to share details of internal deliberations.

Paoletta’s allies say he should be commended for pushing boundaries to help Trump secure wins.

“Will he try to maximize the extent to which the law can be used to advocate for his client’s position? Of course he will — that’s his job,” said Leonard Leo, head of the Federalist Society, a conservative legal organization allied with the administration.

Critics see an attorney who has provided dangerously expansive legal cover for Trump’s willingness to force the law to match his presidential whims.

His unapologetic approach may promise more conflicts ahead, with the administration preparing to release a budget that is likely to provoke another round of skirmishes with Congress and more fights over spending on foreign aid and the border wall.

“From the beginning of the Trump administration, there’s been a real pattern at OMB — from the authority of transfers to building the wall, to the moneys delayed for Puerto Rico — of stretching the budget law,” said Bill Hoagland, a Republican and former staff director on the Senate Budget Committee. “The OMB general counsel is supposed to give his best interpretation of the law to the political operatives there. And it appears to me that — at least on a lot of this — the politics are driving his interpretation, as opposed to the law driving the interpretation.”

Several administration officials defended Paoletta’s work. Two administration officials acknowledged that Paoletta had been forceful in seeking ways to implement the president’s agenda but that he has always relied on the backing of career staffers and stayed within the law. Paoletta is an ally of acting OMB director Russell Vought, and the two have worked closely together in implementing Trump’s agenda.

“Paoletta works well and closely with OMB staff, and his deputy, a career staffer appointed under the Obama administration, has never objected to his legal opinions,” said Rachel Semmel, an OMB spokeswoman.

Paoletta, 57, has spent decades as a conservative operative.

A native of Fairfield, Conn., he quickly gained prominence in conservative legal circles after graduating from Georgetown Law. In 2006, the Wall Street Journal described him as a “mysterious, rather strapping man … looking pretty powerful” while conferring privately with scores of lawmakers. It said of Paoletta: “Picture a square-jawed hockey coach pacing back and forth along the bench, barking at his players from time to time — except this guy’s wearing a suit and, well, whispering.”

Paoletta gained prominence when he helped guide Clarence Thomas through his 1991 Senate confirmation hearings, an effort that eventually secured Thomas’s lifetime appointment to the Supreme Court. Paoletta battled cancer shortly after Thomas’s confirmation and told the Pittsburgh Post-Gazette the new Supreme Court justice called or visited him “every single day.” Paoletta later set up a website devoted to celebrating Thomas.

Paoletta later went to Capitol Hill, where he served as chief counsel for oversight and investigations with the House Energy and Commerce Committee. He led probes of Enron and Martha Stewart. Paoletta left the Hill to join various lobbying firms and did legal work related to Major League Baseball’s steroids scandal. He joined a “truth squad” for Sarah Palin, Sen. John McCain’s vice-presidential nominee, to defend her from criticisms in the media.

His professional approach crystallized as it hardened with experience.

“Grab the offense,” Paoletta wrote in one internal strategy memo on Thomas’s circuit court hearings kept by the George H.W. Bush Presidential Library. “Mold the candidate in our image; not the opposition’s.”

His style has led to some internal conflict.

Early in the Trump administration, Paoletta’s relationship with other White House officials fractured over another Supreme Court nominee, Neil M. Gorsuch, Trump’s first appointment to the high court. At the time, Paoletta was working as a counsel to Vice President Pence and wanted to be involved in preparing Gorsuch for his confirmation hearings, although some White House officials were against it. He had clashed at times with then-White House Counsel Donald McGahn, who was leading the process.

But his involvement proved critical, said Mike Davis, a former top counsel for Sen. Charles E. Grassley (R-Iowa) who worked with Paoletta during the Gorsuch confirmation. Paoletta asked “really tough questions that prepared the nominee for game day,” Davis said.

Gorsuch personally thanked Paoletta by name when he was sworn in. Paoletta left Pence’s office not long thereafter and joined the OMB at the beginning of 2018 at the invitation of Mick Mulvaney, who was heading the budget office at the time and is now acting White House chief of staff.

Paoletta’s legal moves at the OMB ignited multiple controversies, but public attention rarely fell on him. In the spring and summer of 2018, he helped push forward a package of “rescissions” that would claw back billions in funding already approved by Congress but not yet spent. Paoletta helped develop the plan, according to government officials, relying on a little-known legal tool that had fallen into disuse. It met bipartisan opposition and failed in the Senate.

Within months Paoletta was involved in another showdown with Congress, this time over funding for Trump’s border wall.

During the record-long government shutdown a year ago, Paoletta worked with federal agencies to figure out how to limit the impact of the shutdown on government services, including by keeping many of the nation’s parks open. That led the Government Accountability Office, an investigative agency that reports to Congress, to accuse the Interior Department of violating the law by using recreation fees to keep national parks running in absence of congressional appropriations. Paoletta brushed the GAO criticism aside, arguing the office, as a legislative-branch agency, has no jurisdiction and can be ignored.

“That’s pretty atypical,” said Ilona Cohen, who served as OMB general counsel during the final years of the Obama administration. “It’s not that reasonable people can’t disagree, but it’s pretty atypical for them just to say we’re not going to listen to GAO.”

As the shutdown ended, Paoletta pushed for a controversial interpretation of the law that would allow the White House to redirect military funds so that Trump could build his border wall, over the objections of Republicans and Democrats.

Internally, White House Counsel Pat Cipollone argued against what Paoletta proposed and warned that it could be illegal, according to an administration official who spoke on the condition of anonymity to discuss internal debates. Paoletta moved forward anyway, with Trump’s support. The Justice Department’s Office of Legal Counsel also signed off on the decision, but multiple Republicans voted against the White House’s move in a congressional resolution later vetoed by Trump.

The Ukraine aid delay may be where Paoletta’s influence has most clearly emerged. He worked closely throughout the saga with Vought, administration officials said, signing off on the language holding up the funds and working with attorneys at the Pentagon.

Some Defense Department officials warned against delaying the assistance, however, according to testimony in the House impeachment inquiry. During the inquiry, Paoletta reviewed OMB emails and helped draft talking points defending the administration’s position, according to an administration official and internal documents. Paoletta’s name appears dozens of times in batches of emails about the Ukraine decision released under Freedom of Information Act requests, though usually the content is redacted. Paoletta also reviewed the redactions, the administration official said.

Paoletta and other political appointees overruled concerns expressed by career staffers who feared that delaying the Ukraine money might result in a violation of the Impoundment Control Act, a Nixon-era law that limits the ability of the executive branch to change Congress’s spending decisions, according to congressional testimony and people briefed on the actions.

Earlier this month, the GAO ruled that the delay did violate that law. And the GAO criticized Paoletta’s justifications for the delay, which he laid out in a nine-page memo in December asserting that OMB’s actions were a routine “exercise of its statutory authority.”

That claim, the GAO said, had “no basis in law.”

Semmel, the OMB spokeswoman, disputed the agency’s findings.

“We disagree with GAO’s opinion,” she said. “OMB uses its apportionment authority to ensure taxpayer dollars are properly spent consistent with the president’s priorities and with the law.”

Among the career staffers flagging concerns about the Ukraine delay was Mark Sandy, a senior OMB official who was the only agency employee to testify for impeachment investigators about the Ukraine matter. Multiple top political appointees had defied congressional subpoenas.

Paoletta has repeatedly expressed skepticism about Sandy, according to people who have heard his comments and said they were part of a pattern of coming into conflict with career staffers. Sandy’s attorney declined to comment.

Paoletta has suggested that career employees who are not moving quickly enough are seeking to undermine the president’s agenda, according to administration officials and others familiar with his actions.

In November, some of Paoletta’s allies were pushing for him to take a lead role in Trump’s impeachment defense. Clarence Thomas’s wife, Ginni Thomas, released a statement to the Washington Examiner in support of the idea, even though Paoletta had never sought the role. Administration officials said Mulvaney wanted Paoletta on the impeachment team as well, but Cipollone was opposed.

Paoletta was ultimately blocked. He has remained at the budget agency while Cipollone and others have taken the public stage defending some of the legal moves that Paoletta helped orchestrate.