President Trump has nominated William Barr to be the next Attorney General. Photo by Bill Clark/CQ Roll Call.

WASHINGTON — Attorney General William P. Barr said Monday that he saw no reason to appoint special counsels to oversee the Justice Department’s ongoing criminal investigation into Hunter Biden, son of President-elect Joseph R. Biden, Jr., or to investigate President Trump’s baseless claims of widespread voter fraud, again undercutting Mr. Trump’s efforts to bend the department to his political will and to overturn the results of the election.

At a news conference to announce charges in an unrelated terrorism case, Mr. Barr said that he did not “see any reason to appoint a special counsel” to oversee the ongoing investigation into the younger Mr. Biden.

“I have no plan to do so before I leave,” Mr. Barr said. ”To the extent that there is an investigation, I think that it’s being handled responsibly and professionally.”

He also said that he would name a special counsel to oversee an inquiry into election fraud if he felt one was warranted. “But I haven’t and I’m not going to,” Mr. Barr said. He added that he saw “no basis” for the federal government to seize voting machines.

Mr. Barr’s comments are sure to further poison his relationship with Mr. Trump, who has expressed rage that Mr. Barr has not done more to help him overturn the results of the November election.

Mr. Barr has long been regarded as Mr. Trump’s most loyal and effective cabinet member, who on several occasions made decisions that directly benefited Mr. Trump and his allies. But his relationship with the president fractured in the wake of the election after he publicly said that he had not seen enough voter fraud to change the election’s outcome and it became clear that he had kept the ongoing investigation in Mr. Biden’s son under wraps.