US knows the weapons would promptly end up captured or smuggled into Russian hands
Ukrainian President Petro Poroshenko disclosed in an interview with a Ukrainian news channel why the EU and the US have refused to provide weapons to Ukraine, saying, “I was given two reasons. First, you don’t have an army. What you do have is infiltrated by Russian agents, and everything we give you will end up in Russia. And second, [the army] is corrupt.”
In March 2015, Poroshenko announced that Ukraine had signed weapons trade contracts with EU states. He said that “if there will be a new wave of aggression against Ukraine, I can say with confidence that it will quickly be met with lethal weapons and a new wave of sanctions against the aggressor.”
In June, it was reported that Ukraine would receive lethal weapons from 11 states.
After the conflict in Ukraine began, the US started delivering body armor, night vision gear, medical supplies, and radio supplies to Ukraine. In late March, Ukraine got its first shipment of American Humvees.