A history lesson for Trumpettes.
Since 1991, the U.S. has sought to guarantee Ukraine's independence and security, seeing it as a key bridge between East and West.
When the USSR dissolved, Ukraine inherited the third-largest nuclear arsenal in the world, with some 1,900 strategic nuclear weapons pointed at the United States.
Keen to avoid a proliferation of nuclear powers, the U.S., U.K., and Russia in 1994 signed the Budapest Memorandum, which transferred the weapons to Russia in exchange for a commitment by Washington, Moscow, and London to "respect the independence and sovereignty and existing borders of Ukraine" and to "refrain from the threat or use of force" against it.
Russia continued meddling in Ukrainian politics, though, and overtly broke the treaty in 2014 when it annexed Crimea.
Trump was perfectly willing to blow up this important alliance with Ukraine if President Zelensky refused to do him a personal/political favor.