WASHINGTON — A federal judge blocked AT&T’s move to obtain communication logs between the Justice Department and the White House on Tuesday, hampering the phone giant’s argument that politics played a role in the government’s decision to halt a merger with Time Warner.

Judge Richard J. Leon of U.S. District Court in Washington, who is overseeing a trial over the deal, said AT&T did not sufficiently show in pretrial discussions that it was treated differently from other companies.

“Defendants have fallen far short of establishing that this enforcement action was selective,” Leon said.

The decision puts a crimp in AT&T’s defense for its $85 billion proposed merger with Time Warner. It is a big win for the Justice Department, which would like to avoid attention on the role of politics in its decision to stop the deal. The merger would transform the media landscape by combining a television and movie giant with one of the nation’s biggest media distributors.

“We respect the judge’s decision and look forward to the upcoming trial,” said Dan Petrocelli, lead trial lawyer for both Time Warner and AT&T.

In a statement, the Justice Department said, “We are pleased with and respect today’s decision, which will permit the parties and court to focus on the case at hand.”

AT&T has argued that the Justice Department has unfairly singled out its proposed merger with Time Warner partly to stay in favor with the White House. President Donald Trump has been a vocal critic of Time Warner’s news network, CNN, and said before the election that the deal should be stopped.

AT&T’s lawyers have requested emails, phone and other communications logs between Justice Department officials and the White House, to see if the White House influenced the agency’s decision.

Last week, the Justice Department asked Leon to block the company’s demands for communications with the White House, saying they were a “sideshow” to the antitrust concerns. The Justice Department has argued that consumers would be harmed by the deal, saying it would stifle competition and lead to higher consumer prices.

The blockbuster trial will begin March 19.