Ukraine has a future. And the West has a crucial role to play in what that future looks like. Recently, I joined a group of Western security experts on a trip to Ukraine organized by the Warsaw-based Polish Institute of International Affairs. We met with the Ukrainian president. We visited Bucha, the high-water mark of the Russian incursion toward Kyiv, where the invaders massacred hundreds of civilians. We saw a lot in a few days — but anyone who spends a few days in a war zone and then claims to know exactly what is going on is talking nonsense. Nonetheless, the state of what is now a very long war is clear, as are America’s obligations and opportunities. For starters, it is in the interest of the West, particularly the United States, to see...