"When Coors merges with Miller Lite, there will be an effect on the price of both Coors and Miller Lite, though it might be too small to be of concern. But the very fact that some Coors drinkers would switch to Miller if Coors were to increase the price of Coors (and vice versa) is enough to give rise to an effect," said Hay. "The judge didn’t get that."
In other words, Judge Leon ruled the merger's effect on prices would be insignificant. But if an appeals court says the more important point is that there simply would be any effect and that even a small potential jump in price would be bad for consumers, the DOJ has a shot, Hay said.
If the DOJ does win, AT&T can then ask the Supreme Court to take on the case. It would be the first vertical integration case the Supreme Court has heard since 1972, when the Court ruled Ford Motor could not acquire certain assets of Electric Autolite because of competitive harm. That case, however, showed much clearer consumer harm than AT&T's purchase of Time Warner, Breed said.
If the case were to be sent to the Supreme Court, a ruling likely wouldn't come until 2020 at the earliest, Breed said. That means DOJ would operate under the standards it used to block AT&T's deal for Time Warner until then.
It's unclear what a DOJ win would mean for the near-term future of Warner Media. AT&T has put a self-imposed division between itself and Turner's cable networks, including CNN, TBS and TNT, which would make a theoretical unwinding of the merger easier.
"AT&T Communications will have no role in setting Turner's prices or other terms to unaffiliated distributors, and Turner will not consult with AT&T Communications in setting Turner prices or other terms for programming provided to unaffiliated video distributors," AT&T said when it closed the Time Warner deal.
Still, AT&T CEO Randall Stephenson told CNBC Friday that he expected an appeal and that the decision won't change his company's integration plan with Warner. AT&T has already acquired advertising technology platform AppNexus to improve online video targeting. And AT&T executive John Stankey outlined a new trajectory for HBO that includes more investment and different kinds of content to better compete with Netflix.
"This changes nothing we'll be doing over the next 30 days or the next 12 months," Stephenson said. "We think the likelihood of this thing being reversed and overturned is really remote."
Disclosure: Comcast is the owner of NBCUniversal, parent company of CNBC and CNBC.com.