While it is normal for the Justice Department to be involved in antitrust issues, the fate of CNN in this particular case raises questions about whether the president is trying to influence the outcome, given his very public opinion of the news network.

During the 2016 campaign, Mr. Trump said his administration would not let such a deal go through.

Shortly before criticizing CNN on Wednesday, Mr. Trump promoted an upcoming report about his Asia trip on Fox News Channel, a network much more to his liking.