Ever since Donald Trump was elected President of the United States and declared, shortly afterward, “The law’s totally on my side, the President can’t have a conflict of interest,” the hopes of those concerned about government integrity have resided largely in one man: Walter Shaub, the head of the Office of Government Ethics. Although Shaub’s term was set to end in January, 2018, the announcement this week that he is departing his post five months early was greeted with concern by ethics watchers. In their view, Shaub and people like him are urgently needed.

“Public service is a public trust,” Shaub wrote in his resignation letter, one requiring “employees to place loyalty to the Constitution, the laws and ethical principles above private gain.”

One of the gravest concerns that has weighed on ethics watchers over the last six months is the disquieting sense that Trump and his family are using his time in the White House to enrich themselves, a fear which Trump has done little to assuage. As of July 4th, the President had visited a Trump-branded property forty-nine out of his hundred and thirty-three days in office, according to the Washington Post, providing a running product placement for his Presidency, while a lawsuit filed by the attorneys general of Maryland and D.C. asserts that the Trump International Hotel in Washington has “specifically marketed itself to the diplomatic community” since the Presidential election. The suit also mentioned the troubling implications of Trump-branded real-estate projects that are proceeding in the United Arab Emirates and Indonesia. In an interview on CBS News on Thursday evening, Shaub clarified some of his thoughts. “I can’t know what their intention is,” he said of the Trumps. “I know that the effect is that there’s an appearance that the businesses are profiting from his occupying the Presidency. And appearance matters as much as reality. So, even aside from whether or not that’s actually happening, we need to send a message to the world that the United States is gonna have the gold standard for an ethics program in government, which is what we’ve always had.”

He also said, “I really feel like I’ve achieved all I can achieve under the current circumstances.”

In the past, the Office of Government Ethics was a quiet, not terribly exciting place whose director’s name was rarely known among the public; under Trump, the office was transformed into a place of urgency. Shaub has served as the only independent voice inside the government, monitoring the many conflicts of interest that surround Trump, and as a regular source of pressure and publicity around the Administration’s many ethics violations. He has shown through his actions that he regards his role as that of a guardian of the public interest in the purest sense. Most recently, Shaub criticized the Administration’s attempt to keep secret its decision to grant dozens of waivers that allowed government officials to circumvent the Administration’s own ethics rules. When, under pressure from Shaub, the waivers were made public, Shaub was quick to point out that some waivers had been, essentially, backdated to the beginning of Trump’s Presidency and might not even be valid. “If you need a retroactive waiver, you have violated a rule,” he told the Times.

His most powerful public comments came after Trump decided that he would break with Presidential precedent and retain full ownership of his real-estate and branding companies while in office. Previous Presidents have divested themselves of their business interests or put their assets in a blind trust, managed by a third party, over which they had no control. The President pledged to place his ownership interest in a trust and hand the day-to-day operational-management duties over to his sons, which, Shaub noted, assuredly and publicly, was largely a cosmetic decision. “This is not a blind trust,” he said at the time. “Not even close.”

Shaub also took issue with Trump’s claim that he couldn’t sell his business, which most ethics experts said would come closest to resolving his conflicts, because it would be complicated to try to sell off a company based on his own brand and he might lose money in the process. As President, there are many policies Trump is involved in that could materially affect his company—rewriting the tax code; changing environmental or trade rules; developing relationships with countries in which the Trump Organization manages or licenses properties, or hopes to in the future. Continuing to collect revenue from the Trump Organization while making decisions as President that could affect the company would have an irreparable, cheapening effect on the office of the President: “We can’t risk creating the perception that government leaders would use their official positions for profit,” Shaub said.

After leaving his post at the O.G.E., Shaub will join the Campaign Legal Center, a nonpartisan organization based in Washington, D.C., as the director of its ethics program. According to Lawrence Noble, the Center’s general counsel, Shaub learned about the job opening only recently. “When the opportunity came for us to hire Walt, we couldn’t pass it up,” Noble said. He added that, to the best of his knowledge, Shaub “was under no outside pressure” to leave the O.G.E. before his term ended, and Shaub told the Washington Post much the same.

In his new role, Shaub will be helping the Center to expand its ethics program, strengthen its watchdog role, and help design potential fortifications to the ethics rules, which have been “stress-tested” under President Trump, as Noble put it. He added that Trump had exposed many weaknesses in ethics laws. With Shaub’s help, his organization will be looking at ways to strengthen and update conflict-of-interest rules for the President specifically, as well as ways to potentially give more power to the O.G.E., which, currently, can only offer advice and suggestions and has no enforcement role.

Shaub made the best use of his advisory role as he could. As my colleague Ryan Lizza described, after Trump revealed his plan for keeping his business assets, Shaub gave a speech at the Brookings Institution in which he tried to appeal to the President to set a better example. “It’s important to understand that the President is now entering the world of public service,” Shaub said in that speech. “He’s going to be asking his own appointees to make sacrifices. He’s going to be asking our men and women in uniform to risk their lives in conflicts around the world. So, no, I don’t think divestiture is too high a price to pay to be the President of the United States of America.”

If there is one thing to worry about surrounding Shaub’s departure from government, it is whether the next head of the Office of Government Ethics will use his or her position in the same fashion in the future. “I hope he selects someone who is dedicated to the mission of the office, but we’ll see,” Noble said. “I am waiting to see what he does, anxiously.”