Zelenskyy has a gamechanging plan to win peace. For it to work, Biden must back it – fast | Timothy Garton Ash

In besieged Kharkiv, I saw how Ukraine is approaching a perilous moment. To turn the tide, it first needs to decisively knock back Russia

Earlier this week, I started a 3,000km, two-day journey back from the other end of Europe, where I witnessed Ukrainian resilience against Russian terror in the besieged city of Kharkiv. A university lecturer told me that from a 12th storey balcony in a north-eastern suburb she had actually seen the flashes of missiles taking off from launchpads just across the frontier, in the Russian city of Belgorod. An S-300 missile can reach Kharkiv from Belgorod in about 30 seconds, so you have no time to hide. If it's not a missile, it's a glide bomb launched from a Russian warplane - and so, day after day, death rains indifferently down.

After more than 900 days of the largest war in Europe since 1945, Ukraine is approaching a perilous moment of truth. The Ukrainian David has courage and innovation, but the Russian Goliath has ruthlessness and mass. In an underground location in Kharkiv, I was shown highly sophisticated, novel military uses of IT and drones. With its Cossack-style innovation, the country has developed more than 200 different kinds of drone.

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