The DOJ should be even more likely to shoot down a horizontal merger that consolidates an industry with four participants to three, as in the case of T-Mobile-Sprint, says Ketan Jhaveri, a former DOJ trial attorney and antitrust lawyer at Simpson Thacher & Bartlett.
"Anyone would tell you suing to block a vertical deal, which is much more complicated, and not blocking a horizontal case would be a weird way to decide antitrust policy," Jhaveri said. "But we're living in a time where these contradictions may not matter anymore."
Jhaveri gives the deal a 40 percent chance of approval but said it would have had only a 10 percent chance in an Obama administration.
The approval of T-Mobile-Sprint will hinge on a classic antitrust question: do regulators think a deal will mean higher prices for consumers?
One antitrust watcher thinks the risks of an government block are high.
A deal "would increase concentration significantly in the highly concentrated mobile wireless market, creating a structural dynamic that positions the deal with a difficult path to antitrust clearance," according to an April 30 note to clients from The Capital Forum, a news and analysis firm dedicated to government regulators.
"Little has changed on the competitive merits since August 2014, when the companies abandoned merger talks in response to DOJ and FCC opposition" says Teddy Downey, The Capitol Forum's executive editor and CEO.
However, if Judge Leon does allow AT&T to buy Time Warner, T-Mobile and Sprint's chances greatly improve, according to Wagner, the Federal Bar Association's antitrust chair.
AT&T will be that much bigger and stronger, strengthening the argument that Sprint and T-Mobile can only compete by coming together.
"It's never a safe bet to say a 4-to-3 consolidation will get approved, but Sprint and T-Mobile have a better argument than most," Wagner said. "They'll argue that AT&T and Verizon are such behemoths that they only way they can bring down prices for everyone, not just their own customers, is to get big enough to really put pressure on them."
A loss for the DOJ may also make the regulatory body gun-shy to block another deal, Wagner said.
"Regulators don't like to lose," Wagner said. "They won't want to take two big losses in a row."
But if Judge Leon does shoot down AT&T-Time Warner, all bets are off. It could be back to the drawing board for the entire industry.
Disclosure: Comcast is the owner of NBCUniversal, the parent company of CNBC and CNBC.com.