Biden is walking a tightrope with Ukraine. What’s his next step? | Christopher S Chivvis

America and Europe's response to the war is already unprecedented in military, economic and political terms - what should they do now?

The United States and its allies need to strike a balance between making Putin's appalling invasion in Ukraine as costly as possible, while avoiding uncontrolled escalation that could lead to a much broader and more dangerous war. So far, the White House has managed to walk this tightrope, but it's almost certain to grow harder the longer the war goes on, as Volodymyr Zelenskiy's impassioned address to the US Congress on Wednesday demonstrated.

Naturally, for the Ukrainian president, the more involved Nato gets, the better. Ukraine's chances of repelling the Russian invaders on the battlefield may be slim, but with luck and the world's support, there's still hope that he will survive long enough that Putin has no alternative but to negotiate an end to war that leaves Ukraine's sovereignty intact. Right now, this seems like the best of any realistic outcome.

Christopher S Chivvis is a senior fellow and director of the Carnegie Endowment's American statecraft program