expanding appellate litigation practice. As part of King & Spalding, he argued on behalf of the NRA in the Supreme Court case McDonald v. Chicago on March 2, 2010. Clement was part of the legal team that represented NBA players in labor negotiations during the 2011 lockout. Clement also advised 10 NFL players in the spring of 2011 when the NFL was facing a potential lock-out. As a partner at King & Spalding, Clement was hired in April 2011 by the Republican majority in the U.S. House of Representatives to defend the Defense of Marriage Act, a law that defined marriage as between one man and one woman, after the U.S. Department of Justice chose to stop defending it. King & Spalding withdrew from the case on April 25, 2011, and Clement resigned from the firm to continue his representation, arguing that "representation should not be abandoned because the client's legal position is extremely unpopular in certain quarters." Clement joined Bancroft PLLC, a boutique law firm led by former Assistant Attorney General Viet D. Dinh. Clement led the challenge on behalf of 26 states to overturn the Patient Protection and Affordable Care Act in the Supreme Court on March 26–28, 2012. The Court upheld the "individual mandate" as a tax, but found the States could not be compelled to follow the portion of the law relating to Medicaid expansion. On March 27, 2013, Clement served for the respondent Bipartisan Legal Advisory Group of the United States House of Representatives at the Supreme Court in United States v. Windsor. On June 26, 2013, the Court ruled against Clement and BLAG by finding the Defense of Marriage Act to be unconstitutional. Clement was mentioned as a potential Supreme Court nominee of Republican presidential nominees John McCain and Mitt Romney. In 2014, Jeffrey Toobin named Clement a likely Supreme Court nominee in the event of a Republican victory in the 2016 presidential election. In 2019, Clement was an attorney for the appellants in the landmark Rucho v. Common Cause Supreme Court case, in which partisan gerrymandering was declared a non-justiciable issue. In September 2020, Clement joined the list of President Donald Trump's potential Supreme Court candidates. In June 2022, following his clients' Supreme Court victory in New York State Rifle & Pistol Association, Inc. v. Bruen, Clement separated from Kirkland & Ellis, after the firm announced it would "no longer handle Second Amendment