“Since the beginning of the war in Ukraine more than two years ago, US and Western military assistance to the country has followed a pattern.
First, Kyiv asks for a particular weapons system or capability. Washington declines due to concerns about raising the risk of escalation with Russia. Vladimir Putin then makes vague threats involving his nuclear arsenal. Ukraine’s advocates respond by spending months making their case in the media. One or several European allies come around to giving the Ukrainians what they want, and then eventually the US does as well.
This is more or less what happened with the debate over providing Ukraine with battle tanks, Patriot air defense systems, F-16 fighter jets, and long-range ATACMS, among other systems.”
https://www.vox.com/world-politics/353796/us-weapons-ukraine-russia-putin-escalation-nuclear