“He’s not wrong there,” Mr. Poroshenko responds with a smile, digging into the cold cuts that the flight attendant has just brought to him. “But make no mistake: The time is long past when the navy at Sebastopol and the barracks at Belbek and Novofedorivka gave up without firing a shot. That’s the only advantage of war: You learn how to wage it.”

I also tell him that many in the U.S. and Europe doubt the capacity of his soldiers to make good use of the sophisticated weapons that eventually may be delivered to them. At this, he guffaws and, after exchanging a few words in Ukrainian with his chief of staff, says:

“Well, tell them, please, that they’ve got it wrong. We would need a week, no more, to take full possession of the equipment. Know that, because we had no choice, our army is about to become the best, the bravest, and the most hardened force in the region.”

From that point on, he darkens again only when I mention the uphill battle that his American friends will have to fight before any equipment can be delivered: Congress will have to reapprove the Ukrainian Freedom Support Act that it first passed on Dec. 11. It is an appropriation bill to release the $350 million in military aid that was approved. Final approval will be needed from President Obama, whose tendency to procrastinate in such matters is well known. And a decision will need to be made about whether the equipment can be taken from existing stocks or will have to be manufactured, which would take even more time.

“I know all that,” Mr. Poroshenko mutters, closing his eyes. “I know. But maybe we’ll get a miracle. Yes, a miracle.”