Three months ago, Corey Lewandowski, President Trump’s first campaign manager, quit a new Washington lobbying firm he had helped start after the election, amid scrutiny over his firm’s clients and his extraordinary access to Mr. Trump. But Mr. Lewandowski’s departure from the influence business did not last long.

About a week after leaving his old firm, Mr. Lewandowski started a new consulting business, according to corporate filings. And now, as he takes on an increasingly broad role as an unofficial White House adviser, he is building a roster of clients with major interests before the Trump administration, including an Ohio-based payday lender seeking to block or overturn new federal financial regulations.

Mr. Lewandowski appears to be positioning his new firm as an “advisory” business, part of a growing cohort of Washington influencers who advise companies on how to navigate the government but do not register as lobbyists or disclose their clients. A draft contract obtained by The New York Times stipulates that Mr. Lewandowski’s firm “cannot and will not engage in any lobbying or advocacy services.”

But his new firm once again puts Mr. Lewandowski at the center of the ethical quandaries surrounding the Trump White House, where the president has given significant access and power to friends and loyalists who are not on the government payroll but work as lobbyists or retain significant outside business interests.