Liu entered the 2020 U.S. Championships as the favorite to defend her title. She placed second in the short program after turning out of her triple Axel attempt, but successfully landed a triple flip and a triple Lutz-triple toe combination, as well executing level-4 spins and footwork. She earned 75.40 points, a little over 3.50 points behind Bradie Tennell; she also had a technical base value advantage of more than 16 points over both Tennell and Bell. Skating last and immediately after Mariah Bell's "elegant, near flawless performance" to k.d. lang's version of the Leonard Cohen song "Hallelujah", Liu won the free skate by over eight points, with a score of 160.12, which was her career-best, and 235.52 points overall. Her final score was over 10 points higher than Bell's, who came in second place, and just under 15 points over Tennell's, who came in third. Although she failed to be the first woman at U.S. Nationals to successfully complete a quadruple Lutz, which was called under-rotated and received negative grade of execution scores, her "triple Axels were solid, and her final two spins were of surpassing quality". She landed two triple Axels in the first 65 seconds of her program, and then completed six more triple jumps. Liu told reporters afterwards, "This year I’m thinking, it’s a new decade, like, wow, what a good start!" At the age of 14, Liu's win made her the youngest two-time women's U.S. champion and the first woman in seven years to win back-to-back U.S. championships, since Ashley Wagner in 2012 and 2013 and since Michelle Kwan won 8 consequence titles. Bell and Tennell assisted Liu to the top tier of the podium during the awards ceremony, recreating what they did the previous year. Liu was age-ineligible to compete in international senior-level competitions, but was named to the 2020 World Junior Championships team, alongside Starr Andrews and Lindsay Thorngren.