Peter Keisler. Photo by Diego M. Radzinschi/ALM During the six-week trial over AT&T's planned acquisition of Time Warner, Sidley Austin partner Peter Keisler was a constant presence in court, looking on as O'Melveny & Myers' Daniel Petrocelli mounted a successful defense of the $85 billion deal. advances into a Washington appeals court Keisler, a prominent appellate lawyer who briefly served as interim attorney general late in the George W. Bush administration , entered his first appearance for AT&T late Monday afternoon in the U.S. Court of Appeals for the D.C. Circuit, identifying himself as the lead counsel for a Sidley Austin team that includes Jonathan Nuechterlein and C. Frederick Beckner III, co-leaders of the firm's communications regulatory practice. Also on the Sidley Austin team: Richard Klingler, a partner at the firm who previously served as general counsel on the National Security Council staff during the Bush administration. In Keisler, AT&T has a lawyer who was picked under the Bush administration for a seat on the D.C. Circuit, only to see his nomination scuttled by a Senate filibuster. a month after U.S. District Judge Richard Leon handed down a 172-page opinion rejecting arguments that AT&T's acquisition of Time Warner would substantially lessen competition and hurt consumers. Petrocelli, a seasoned trial lawyer who took up AT&T's case with little to no antitrust experience, has not yet entered an appearance in the D.C. Circuit. Cravath, Swaine & Moore partner Christine Varney, a former head of the Justice Department's Antitrust Division, is representing Time Warner. Keisler previously represented AT&T in the challenge to the Federal Communications Commission's net neutrality rules, which the D.C. Circuit upheld in 2016. Under a Trump-appointed Republican chairman, the FCC later repealed the rules, which required internet services providers to treat all content and traffic equally. In 2016, he argued before the D.C. Circuit for an array of trade associations—including the American Chemistry Council Inc. and U.S. Chamber of Commerce—in a challenge to the Obama administration's Clean Power Plan. For the past two years, the D.C. Circuit has been granting 60-day abeyances in the case as the Trump administration's U.S. Environmental Protection Agency has worked to revise the plan. In its most recent order, the D.C. Circuit revealed that some judges' patience with EPA's regulatory inaction is wearing thin. “ It's a very narrow path that would have to be traveled to get this thing reversed in any way," Stephenson said. "The merger is closed. We own Time Warner."