In recent years, the United States has accused Russia of violating the INF treaty and has tried to force Moscow to comply using sanctions and weapons development. The Russians, however, have refused to adhere to U.S. demands and have accused the United States of violating the treaty. These mutual recriminations have rendered the INF treaty quite vulnerable over the past two decades. But until now, both parties considered the cornerstone arms control agreement, which halted a destabilizing buildup of intermediate-range nuclear missiles in Europe during the 1980s, too pivotal to withdraw from.
But several factors have pushed the United States to its tipping point, including the growing power of China, Russia's continuing INF violations and the ascent of ardent arms-control skeptics in the White House like national security adviser John Bolton. It's possible that the U.S. withdrawal announcement is part of a last-ditch ploy to pressure Russia as Bolton goes there to talk about the INF and other issues (The United States has to notify Russia six months before its formal withdrawal). But the Russians are unlikely to flinch and return to compliance. Indeed, Moscow is actually set to benefit from not being the first party to withdraw from the INF, meaning the demise of the treaty is almost inevitable.
Although the United States and the Soviet Union were the signatories of the INF Treaty, China has increasingly become a key consideration in the treaty's consequences over the past two decades. Not affected by the INF's limits, China has built up a massive land-based arsenal of short- and intermediate-range ballistic and cruise missiles as part of its wider military modernization. This powerful arsenal allows China to challenge U.S. and allied forces in the Western Pacific. And China's growing military capabilities have caused increasing concern for the Russian military, which lacks similar missiles.
While Russia was willing to violate the INF by developing and reportedly fielding some missiles prohibited by the treaty, Moscow was not willing to be the first to abandon the INF outright. This is largely due to the much-improved relationship between Moscow and Beijing over the past few years, which dampened the need for Russia to gear up too dramatically against China. The Kremlin has also been committed to retaining a moral high ground and protecting its reputation as a responsible actor by not being the first to leave the INF.
For the United States — which has begun designing banned weapons but has not yet violated the treaty — China's growing military might was really the largest driver behind the White House's decision to outright withdraw from the treaty. The United States is now considering a major buildup of land-based intermediate-range missiles to challenge China and does not want to be limited by the INF treaty in any way.