WASHINGTON — At the Department of Justice, staff members in the antitrust office have been doggedly investigating AT&T’s blockbuster $85.4 billion bid for Time Warner.

They have deposed the executives of both companies; questioned several media, telecommunications and technology rivals; and demanded thousands of pages of confidential documents from scores of businesses to discern if the deal would violate competition laws — and thus if it should go ahead at all.

But eight months into the review, the small army of career antitrust officials is marching toward a great unknown.

For one thing, the Justice Department officials still don’t have a boss who will have the final say on whether to approve or block the deal. President Trump’s pick for assistant attorney general in charge of antitrust matters, Makan Delrahim, has been held up in a logjam of nominees in the Senate. And Mr. Trump himself, who said during last year’s campaign that he opposed the deal, is another wild card. A senior administration official said last week that members of the White House were discussing how they might use their perch over the merger review as leverage over Time Warner’s news network, CNN.