A high-ranking F.B.I. agent has provided testimony to the House Judiciary Committee that contradicts a key claim made by an I.R.S. agent who said that political interference had hampered the investigation into the taxes of Hunter Biden, the president’s son, dealing a blow to House Republicans’ wide-ranging inquiry into the Biden administration.

In closed-door testimony last week, Thomas Sobocinski, the special agent in charge of the Baltimore Field Office of the F.B.I., told House investigators that David C. Weiss, the U.S. attorney for Delaware overseeing the Justice Department’s inquiry into Hunter Biden, never said he did not have full authority to pursue charges against the president’s son, according to a transcript obtained by The New York Times.

The testimony undercut a key claim from Gary Shapley, a veteran I.R.S. agent turned whistle-blower who has accused the Justice Department of giving Mr. Biden preferential treatment. It also buttressed the account of Mr. Weiss himself, who said he had “never been denied the authority to bring charges in any jurisdiction.”

The news of Mr. Sobocinski’s account, coming on the same day Speaker Kevin McCarthy opened an impeachment inquiry into President Biden, drove home the often shaky nature of the evidence that Republicans are relying on to build a case that the president and his family are part of what Mr. McCarthy called “a culture of corruption.”

House Republicans have relied on Mr. Shapley’s testimony as a basis for their allegations that the Justice Department has stonewalled or slow-walked the investigation into Hunter Biden. Federal prosecutors have indicated that Mr. Biden will face gun and tax charges, but Republicans have said he should have been charged sooner and with more severe counts.

In testimony to Congress detailing his frustrations with how the case was handled, Mr. Shapley said he had witnessed Mr. Weiss “tell a room full of senior F.B.I. and I.R.S. investigators on Oct. 7, 2022, that he was ‘not the deciding person on whether charges are filed.’”

That offended Mr. Shapley because he had watched Attorney General Merrick B. Garland assure the country that Mr. Weiss had the full authority he needed to bring charges.

“That was my red line,” Mr. Shapley testified. “I had seen an undeniable pattern of preferential treatment and obstruction of the normal investigative process.”

But Mr. Sobocinski was also at that meeting, and he told Congress that Mr. Weiss made no such comment.

“If he would have said that, I would have remembered it,” Mr. Sobocinski said in his testimony, which took place on Thursday and was reported earlier by The Washington Post. He added, “I went into that meeting believing he had the authority, and I have left that meeting believing he had the authority to bring charges.”

During the interview, Mr. Sobocinski also pushed back against other claims of political interference. He was asked, “Do you have any reason to believe President Biden interfered in this investigation in any way?”

“No,” he replied.

In a statement, Mr. Shapley’s legal team chalked up the differing testimony to variations in memories from the same event. His lawyers said he had notes to back up his account.

“While it’s not unusual for people to have slightly different recollections of the same event, in this case, S.S.A. Shapley took notes in real time and that day emailed his summary of the meeting to several people, including his supervisor, who contemporaneously corroborated his account — which is all very different from trying to recall information a year later with no notes,” the statement said, using an abbreviation for supervisory special agent.

Mr. Shapley’s lawyers also pointed to the fact that Mr. Garland recently appointed Mr. Weiss as a special counsel, enabling him to bring charges in jurisdictions outside Delaware, as evidence that he had lacked the full authority he needed to prosecute Hunter Biden in California or the District of Columbia, where some of the offenses are alleged to have occurred.

Republicans appeared similarly unmoved.

Russell Dye, a spokesman for Representative Jim Jordan, Republican of Ohio and the chairman of the Judiciary Committee, said Mr. Shapley and a second I.R.S. agent who testified before Congress supporting his account “have been wholly consistent throughout their disclosures to Congress, and the only people who haven’t are people like David Weiss, Merrick Garland and their liberal cronies.”