WASHINGTON — Democrats on the House Judiciary Committee said on Tuesday that they had retained two elite white-collar litigators and prominent legal critics of President Trump to help begin inquiries into some of the most sensitive allegations involving the president, including ethics violations, corruption and possible obstruction of justice.

The committee’s chairman, Representative Jerrold Nadler of New York, has not committed to opening a formal impeachment inquiry. But the addition of the two lawyers, Norman L. Eisen and Barry H. Berke, indicates that the Democrats do not intend to wait for the special counsel, Robert S. Mueller III, to finish his work to begin weighing issues that could ultimately be wrapped up in such a proceeding.

“The president of the United States faces numerous allegations of corruption and obstruction,” Mr. Nadler said in a statement announcing the decision. “His conduct and crude statements threaten the basic legal, ethical and constitutional norms that maintain our democratic institutions. Congress has a constitutional duty to be a check and balance against abuses of power when necessary.”

Mr. Nadler gave little detail about those inquiries in his statement, saying that Mr. Eisen and Mr. Berke would consult on matters “related to the Department of Justice, including the department’s review of Special Counsel Mueller’s investigation.” A Judiciary Committee official, who was not authorized to discuss the appointments publicly, said that Democrats would be making public more detailed plans in the coming weeks.

Retaining two counsels of Mr. Eisen and Mr. Berke’s caliber is relatively unusual for a congressional committee, and it underscores the new legal and political jeopardy the president faces in a House controlled by Democrats. Just in the last week, Democrats in the chamber have begun laying the groundwork to try to obtain Mr. Trump’s long-concealed tax returns and restarted a broad investigation into his ties not only to Russia but also to other foreign entities that could have financial or other leverage over the president or his associates.

Investigators in each inquiry will have the power to call witnesses, demand documents and issue subpoenas to compel evidence — treatment Mr. Trump has already branded “presidential harassment.”

Mr. Eisen served as the top White House ethics lawyer under President Barack Obama and later as his ambassador to the Czech Republic. A former white-collar litigator and investigator, he has emerged since Mr. Trump’s election as one of the president’s most recognizable legal critics, using his perch as chairman of Citizens for Responsibility and Ethics in Washington and a contributor position at CNN to comment voluminously about what he has argued are ethical lapses and instances of outright corruption in the president’s administration.

Mr. Eisen also serves as a co-counsel in a lawsuit accusing Mr. Trump of violating the emoluments clause of the Constitution by refusing to divorce himself from his businesses, and thus reaping financial benefits from foreign agents.

Mr. Berke, a partner at the New York firm Kramer Levin, is less well known in Washington but brings deep connections to the New York legal world, including the federal prosecutors there investigating Mr. Trump’s campaign and inaugural committee. His practice primarily deals with complicated financial and tax crimes, though he has written with Mr. Eisen about obstruction of justice and the president’s other legal vulnerabilities.

Mr. Berke represented Mayor Bill de Blasio of New York in a federal investigation into the mayor’s campaign fund-raising, which concluded in 2017 without charges being filed.

Mr. Eisen resigned from most of his other obligations on Tuesday, and he is expected to drop his role in the emoluments case. Mr. Berke will remain a partner at his firm but spend most of his time working with the Judiciary Committee.

As House committees begin the array of new inquiries, the Judiciary Committee is likely to emerge as a crucial arbiter of Mr. Trump’s political fortunes. It has oversight of the Justice Department and the F.B.I., and has traditionally been the venue where impeachment proceedings begin.

Despite considerable pressure from his left flank, Mr. Nadler has thus far approached the impeachment question cautiously, saying repeatedly that he does not yet see a case and wants to wait for Mr. Mueller to finish his work before proceeding to any formal deliberations.

But he has made some of his views clear.

In recent weeks, Mr. Nadler has said publicly that he believes Mr. Trump “has engaged in a long pattern of obstruction” and views his attacks on federal law enforcement as an existential threat to those institutions.

Mr. Nadler has said that he also plans to investigate Mr. Trump’s role in hush-money payments made shortly before Election Day in 2016 to two women who said they had affairs with Mr. Trump — circumstances that, if true, he said would most likely meet the criteria for an impeachable offense. The president’s former personal lawyer, Michael D. Cohen, implicated Mr. Trump in those payments in court last year as he pleaded guilty to campaign finance and other violations.

Mr. Eisen and Mr. Berke, together with Noah Bookbinder, the executive director of CREW, have written a series of reports and opinion articles on obstruction of justice, collusion and Mr. Trump for the Brookings Institution. Their most recent Brookings report on obstruction, published last August, laid out a case that Mr. Trump’s publicly known actions amounted to obstruction of justice.