Missile, ultimate weapon or long term policy. If I were the US and NATO countries I would want a policy to roll back Russian evil deeds and greed for decades. Would a quick end to the war do that? No. Would a process that sets the war machine back decades and a process to reduce economic power by 40%, well maybe.
First set up the war to efficiently destroy tanks, artillery and logistics. So decades to replace. Second drive the value of oil and gas revenue to 50% lower. Maybe by shifting away from oil and natural gas as quickly as possible. So renewable energy, EVs, heat pumps everywhere asap. Refuse to buy fissile fuel from Russia for US and NATO. Refuse to allow any western technology and investment into Russian fossil fuel infrastructure. Invest in fossil fuel production to increase supply and there reduces prices and profit for Russian competitors. Next encourage destruction of Russian oil infrastructure in the name of Ukraine self defense. Refuse any entry by Russian citizens to western technical education and engineering software.
Ok that should reduce the threat of Russian bad acts and actual damage by about 50% for a few decades. Does this look familiar?