The Justice Department offered no additional comment beyond its filing Thursday.
AT&T General Counsel David McAtee issued a statement defending the original ruling. Its main argument against the merger in the previous case was the possible negative impact on the pay-TV market, where AT&T could restrict access to Time Warner's channels and content for its own benefit and drive up prices.
AT&T defended the merger by arguing that it will allow the company to compete better with Netflix, Amazon, Google and other online video distributors. He said from the bench, "The court has now spoken".
AT&T's acquisition of Time Warner is already underway, so DOJ may also seek an injunction ordering the deal to halt while the appeal is decided on.
The matter now goes to the U.S. Court of Appeals for the District of Columbia Circuit, where a three-judge panel will consider the Justice Department's claims that Judge Leon was incorrect.
CNN has always been a target for Trump, calling the Time Warner-owned news network "fake news".
As a candidate for president, Donald Trump said he opposed the deal, say it would be "too much concentration of power in the hands of too few". Since taking office, Trump has not commented on the deal itself, but in an exclusive interview with Breitbart News previous year he showed amenability to a more aggressive stance on enforcing competition in the media world.
Stung by a federal judge's dismissal of its objections to AT&T's megamerger with Time Warner, the Trump Justice Department is challenging the decision with a legal appeal. "I do not believe that the government has a likelihood of success on the merits of an appeal".