From the Summary: "The United States and Russia signed the New START [Strategic Arms Reduction Treaty] Treaty on April 8, 2010. After more than 20 hearings, the U.S. Senate gave its advice and consent to ratification on December 22, 2010, by a vote of 71-26. Both houses of the Russian parliament--the Duma and Federation Council-- approved the treaty in late January 2011 and it entered into force on February 5, 2011. Both parties met the treaty's requirement to complete the reductions by February 5, 2018. On February 3, 2021, the two parties agreed to extend the treaty for five years, as permitted in the treaty text. [...] The Obama Administration and outside analysts argued that New START strengthens strategic stability and enhances U.S. national security. Critics, however, questioned whether the treaty would serve U.S. national security interests[.] [...] The 2018 Nuclear Posture Review confirmed that the United States would continue to implement the treaty, at least through 2021. The Trump Administration raised questions about the value of the treaty and suggested that the United States might allow it to lapse while negotiating a new treaty that would include Russia and China, and capture all types of Russian nuclear weapons. It eventually sought, but failed, to negotiate a short-term extension in the latter half of 2020. The incoming Biden Administration announced that it would seek a five-year extension of the treaty, and Russia accepted this proposal."
CRS Report for Congress, R41219
Congressional Research Service: https://crsreports.congress.gov/