In Ukraine I saw a brave but ravaged land in limbo. It needs a future – it needs Nato | Timothy Garton Ash

Joe Biden must be bold at this week's summit, and help to give Kyiv the security that would allow it to rebuild

Unless the US gives bolder leadership on long-term security for Ukraine at Nato's Vilnius summit this week, historians may one day ask, Who lost Ukraine?" And their shocking answer might be: President Joe Biden.

I say this after talking to a wide range of people in Kyiv last week, before departing Ukraine on Saturday, the 500th day of the largest war in Europe since 1945. There's still the extraordinary fighting spirit that I found on my last visit, in February. But in five months, some people seem to have aged five years. They are exhausted. The casualties, military and civilian, continue to mount.

Timothy Garton Ash is a historian, political writer and Guardian columnist