Todd Blanche, President Trump’s lawyer and the nominee to be the No. 2 official at the Justice Department, used his confirmation hearing on Wednesday to denounce the investigations and prosecutions of his client as corrupt, and to insist that he would uphold the law.

Mr. Blanche, in delivering his opening statement, did not shy away from his prior role in defending Mr. Trump in court and continued to do so at the hearing.

Referring to what he called unfair treatment of Mr. Trump by prosecutors and judges in court filings and schedules, Mr. Blanche voiced his lingering anger. “I continue to be frustrated,” he said, later adding, “That’s power, and that’s power that’s corrupted.”

The statements were striking given the mounting concerns over the Trump administration’s early moves to fire or reassign dozens of prosecutors and F.B.I. agents. Mr. Trump has complained bitterly about the Justice Department, and said last week that he would dismiss F.B.I. agents, intensifying worries about a possible purge of civil servants viewed as insufficiently loyal to him.

If confirmed as deputy attorney general, Mr. Blanche would have direct oversight of the F.B.I. and other investigative agencies. Department officials often refer to the deputy attorney general as the organization’s “bad cop” because that person settles internal disputes and resolves disciplinary issues.

Asked by Senator Adam B. Schiff, Democrat of California, if he was still Mr. Trump’s lawyer, Mr. Blanche said he was, though he added that there were no active cases he was working on for the president. “My attorney-client relationship with President Trump remains, yes.”